diff --git a/.ci-builds/.azure-exhaustive-tests.yml b/.ci-builds/.azure-exhaustive-tests.yml
index b89e94c4cc4..48b9d7ad23c 100644
--- a/.ci-builds/.azure-exhaustive-tests.yml
+++ b/.ci-builds/.azure-exhaustive-tests.yml
@@ -27,6 +27,9 @@ trigger:
     - KEYS
     - README.md
 
+variables:
+  MAVEN_ARGS: '--show-version --no-transfer-progress'
+
 jobs:
 #-------------------------------------------------------------------------
 # Note: The exhaustive tests can take more than 1 hour to complete.
@@ -41,12 +44,12 @@ jobs:
       lfs: true
       fetchDepth: 10
     - script: |
-        echo "Building ICU4J" && cd icu4j && ant init && ant exhaustiveCheck
+        echo "Building ICU4J" && cd icu4j && mvn install -DICU.exhaustive=10
       displayName: 'Build and Exhaustive Tests'
       env:
         BUILD: ICU4J
     - script: |
-        [ -d icu4j/out/junit-results ] && cd icu4j && cat `find out/junit-results -name "*.txt" -exec grep -l FAILED {} \;`
+        cd icu4j && cat `find . -name surefire-reports -type d -exec grep -l  -r --include="*.txt" FAILED {} \;`
       condition: failed() # only run if the build fails.
       displayName: 'List failures (if any)'
       timeoutInMinutes: 2
diff --git a/.ci-builds/.azure-pipelines.yml b/.ci-builds/.azure-pipelines.yml
index 1903466915f..2ff19b4453d 100644
--- a/.ci-builds/.azure-pipelines.yml
+++ b/.ci-builds/.azure-pipelines.yml
@@ -1,5 +1,8 @@
 # Azure Pipelines (VSTS) configuration for CI builds for ICU.
 
+variables:
+  MAVEN_ARGS: '--show-version --no-transfer-progress'
+
 jobs:
 #-------------------------------------------------------------------------
 - job: ICU4J_OpenJDK_Ubuntu_2204
@@ -13,13 +16,13 @@ jobs:
       lfs: true
       fetchDepth: 10
     - script: |
-        echo "Building ICU4J" && cd icu4j && ant init && ant check && ant localespiCheck
+        echo "Building ICU4J" && cd icu4j && mvn install
       displayName: 'Build and Test'
       env:
         BUILD: ICU4J
     # exit with a non-zero status in order to make this step show as a red X in the UI.
     - script: |
-        [ -d icu4j/out/junit-results ] && cd icu4j && cat `find out/junit-results -name "*.txt" -exec grep -l FAILED {} \;` && exit 1
+        cd icu4j && cat `find . -name surefire-reports -type d -exec grep -l  -r --include="*.txt" FAILED {} \;` && exit 1
       condition: failed() # only run if the build fails.
       displayName: 'List failures (if any)'
 #-------------------------------------------------------------------------
diff --git a/.github/workflows/icu_ci.yml b/.github/workflows/icu_ci.yml
index c47be76808c..b08b3610391 100644
--- a/.github/workflows/icu_ci.yml
+++ b/.github/workflows/icu_ci.yml
@@ -12,6 +12,12 @@ on:
       - 'maint/maint*'
   pull_request:
     branches: '**'
+  workflow_dispatch:
+    # To trigger the Env Test workflow manually, follow the instructions in
+    # https://docs.github.com/en/actions/managing-workflow-runs/manually-running-a-workflow
+
+env:
+  MAVEN_ARGS: '--show-version --no-transfer-progress'
 
 permissions:
   contents: read
@@ -33,8 +39,8 @@ jobs:
            # Regex note: (?! ... ) is a negative lookahead. Succeed if the pattern is not present. 
           set +o pipefail && make doc 2>&1 | tee doxygen.log && ( ! grep -P 'warning:(?! .* file .?Doxyfile)' doxygen.log )
 
-  # ICU4J build and unit test using Ant
-  icu4j-ant-build-and-test:
+  # ICU4J build and unit test using Maven
+  icu4j-mvn-build-and-test:
     strategy:
       fail-fast: false
       matrix:
@@ -54,12 +60,10 @@ jobs:
       - name: ICU4J
         run: |
           cd icu4j;
-          ant init;
-          ant check;
-          ant localespiCheck
+          mvn install
       - name: List failures (if any)
         run: |
-          [ -d icu4j/out/junit-results ] && cd icu4j && cat `find out/junit-results -name "*.txt" -exec grep -l FAILED {} \;`;
+          cd icu4j && cat `find . -name surefire-reports -type d -exec grep -l  -r --include="*.txt" FAILED {} \;`;
         if: ${{ failure() }}
 
   # ICU4J build and unit tests using Maven
@@ -92,7 +96,7 @@ jobs:
           cache: maven
       - name: Run Maven test
         run: |
-          cd icu4j/maven-build;
+          cd icu4j;
           mvn --batch-mode test
 
   # Run `verify` to ensure that `package` (creating .jar files) and `integration-test` (special setup for localespi tests) work
@@ -120,7 +124,7 @@ jobs:
       # integration tests, if any (`integration-test`)
       - name: Run Maven verify
         run: |
-          cd icu4j/maven-build;
+          cd icu4j;
           mvn --batch-mode verify
 
   # ICU4J build and unit test under lstm
@@ -147,16 +151,15 @@ jobs:
       - name: ICU4J
         run: |
           cd icu4j;
-          ant init;
-          ant check;
-          ant localespiCheck
+          mvn install
       - name: List failures (if any)
         run: |
-          [ -d icu4j/out/junit-results ] && cd icu4j && cat `find out/junit-results -name "*.txt" -exec grep -l FAILED {} \;`;
+          cd icu4j && cat `find . -name surefire-reports -type d -exec grep -l  -r --include="*.txt" FAILED {} \;`;
         if: ${{ failure() }}
 
   # ICU4J build and unit test under adaboost
   adaboost-icu4j-build-and-test:
+    if: false # Temporary disable, until we disable the .jar creation from C and distribute the individual files
     runs-on: ubuntu-latest
     steps:
       - name: Checkout and setup
@@ -179,12 +182,10 @@ jobs:
       - name: ICU4J
         run: |
           cd icu4j;
-          ant init;
-          ant -Dcom.ibm.icu.impl.breakiter.useMLPhraseBreaking=true check;
-          ant localespiCheck
+          mvn -Dcom.ibm.icu.impl.breakiter.useMLPhraseBreaking=true install
       - name: List failures (if any)
         run: |
-          [ -d icu4j/out/junit-results ] && cd icu4j && cat `find out/junit-results -name "*.txt" -exec grep -l FAILED {} \;`;
+          cd icu4j && cat `find . -name surefire-reports -type d -exec grep -l  -r --include="*.txt" FAILED {} \;`;
         if: ${{ failure() }}
 
   # gcc debug build.
diff --git a/.github/workflows/icu_merge_ci.yml b/.github/workflows/icu_merge_ci.yml
index 9e3d963af61..7e3c4146a8e 100644
--- a/.github/workflows/icu_merge_ci.yml
+++ b/.github/workflows/icu_merge_ci.yml
@@ -10,6 +10,12 @@ on:
     branches:
       - main	
       - 'maint/maint*'
+  workflow_dispatch:
+    # To trigger the Env Test workflow manually, follow the instructions in
+    # https://docs.github.com/en/actions/managing-workflow-runs/manually-running-a-workflow
+
+env:
+  MAVEN_ARGS: '--show-version --no-transfer-progress'
 
 permissions:
   contents: read
@@ -38,8 +44,8 @@ jobs:
           mkdir /tmp/icu4j_data_test;
           cp -P data/out/tmp/icudt*l* /tmp/icu4j_data_test/
           cd ../../icu4j;
-          ant clean;
-          ant -Dicu4c.data.path=/tmp/icu4j_data_test check;
+          mvn clean;
+          mvn -Dicu4c.data.path=/tmp/icu4j_data_test install
 
   # Compile libraries used by all ICU4C performance tests.
   icu4c-store-perf-libs:
@@ -294,12 +300,11 @@ jobs:
           git restore --staged tools/multi/proj/icu4cscan/old-xmls.tar.bz2;
           git restore tools/multi/proj/icu4cscan/old-xmls.tar.bz2;
           cd icu4j;
-          ant;
-          ant perf-tests;
+          mvn install -DskipITs -DskipTests;
           git status
           cd perf-tests;
           mkdir -p perf/results/j_unicodesetperf/${{ matrix.perf }};
-          java -cp ./out/bin:../tools/misc/out/bin/:../icu4j.jar com.ibm.icu.dev.test.perf.UnicodeSetPerf ${{ matrix.perf }} -a -t 2 -p 4 [:Lt:] | tee perf/results/j_unicodesetperf/${{ matrix.perf }}/output.txt
+          java -cp ../tools/misc/target/:../../icu4j/main/icu4j/target/ com.ibm.icu.dev.test.perf.UnicodeSetPerf ${{ matrix.perf }} -a -t 2 -p 4 [:Lt:] | tee perf/results/j_unicodesetperf/${{ matrix.perf }}/output.txt
 
       - name: Store performance test results
         uses: gregtatum/github-action-benchmark@d3f06f738e9612988d575db23fae5ca0008d3d12
@@ -348,11 +353,10 @@ jobs:
           git restore --staged tools/multi/proj/icu4cscan/old-xmls.tar.bz2;
           git restore tools/multi/proj/icu4cscan/old-xmls.tar.bz2;
           cd icu4j;
-          ant;
-          ant perf-tests;
+          mvn install -DskipITs -DskipTests;
           cd perf-tests;
           mkdir -p perf/results/j_ucharacterperf;
-          java -cp ./out/bin:../tools/misc/out/bin/:../icu4j.jar com.ibm.icu.dev.test.perf.UCharacterPerf -a -t 2 -p 4 0 ffff | tee perf/results/j_ucharacterperf/output.txt
+          java -cp ../tools/misc/target/:../../icu4j/main/icu4j/target/ com.ibm.icu.dev.test.perf.UCharacterPerf -a -t 2 -p 4 0 ffff | tee perf/results/j_ucharacterperf/output.txt
 
       - name: Store performance test results
         uses: gregtatum/github-action-benchmark@d3f06f738e9612988d575db23fae5ca0008d3d12
@@ -404,15 +408,14 @@ jobs:
           git restore --staged tools/multi/proj/icu4cscan/old-xmls.tar.bz2;
           git restore tools/multi/proj/icu4cscan/old-xmls.tar.bz2;
           cd icu4j;
-          ant;
-          ant perf-tests;
+          mvn install -DskipITs -DskipTests;
           cd perf-tests;
           mkdir -p perf/results/j_decimalformatperf/${{ matrix.locale }}/${{ matrix.perf }};
           # Delay execution by random number of seconds. Spreading execution of multiple
           # tests over 180 secs. minimizes the possibility of push conflicts when storing
           # tests results in the data branch.
           sleep $(($RANDOM % 180));
-          java -cp ./out/bin:../tools/misc/out/bin/:../icu4j.jar com.ibm.icu.dev.test.perf.DecimalFormatPerformanceTest ${{ matrix.perf }} -a -t 2 -p 4 -L ${{ matrix.locale }} "#,###.##" "1.234,56" -r 1 | tee perf/results/j_decimalformatperf/${{ matrix.locale }}/${{ matrix.perf }}/output.txt
+          java -cp ../tools/misc/target/:../../icu4j/main/icu4j/target/ com.ibm.icu.dev.test.perf.DecimalFormatPerformanceTest ${{ matrix.perf }} -a -t 2 -p 4 -L ${{ matrix.locale }} "#,###.##" "1.234,56" -r 1 | tee perf/results/j_decimalformatperf/${{ matrix.locale }}/${{ matrix.perf }}/output.txt
 
       - name: Store performance test results
         uses: gregtatum/github-action-benchmark@d3f06f738e9612988d575db23fae5ca0008d3d12
@@ -467,15 +470,14 @@ jobs:
           git restore --staged tools/multi/proj/icu4cscan/old-xmls.tar.bz2;
           git restore tools/multi/proj/icu4cscan/old-xmls.tar.bz2;
           cd icu4j;
-          ant;
-          ant perf-tests;
+          mvn install -DskipITs -DskipTests;
           cd perf-tests;
           mkdir -p perf/results/j_normperf/${{ matrix.source_text }}/${{ matrix.perf }};
           # Delay execution by random number of seconds. Spreading execution of multiple
           # tests over 180 secs. minimizes the possibility of push conflicts when storing
           # tests results in the data branch.
           sleep $(($RANDOM % 180));
-          java -cp ./out/bin:../tools/misc/out/bin/:../icu4j.jar com.ibm.icu.dev.test.perf.NormalizerPerformanceTest ${{ matrix.perf }} -a -t 2 -p 4 -f $DATA_FILE_PATH/${{ matrix.source_text }}.txt -e UTF-8 ${{ matrix.mode }} | tee perf/results/j_normperf/${{ matrix.source_text }}/${{ matrix.perf }}/output.txt
+          java -cp ../tools/misc/target/:../../icu4j/main/icu4j/target/ com.ibm.icu.dev.test.perf.NormalizerPerformanceTest ${{ matrix.perf }} -a -t 2 -p 4 -f $DATA_FILE_PATH/${{ matrix.source_text }}.txt -e UTF-8 ${{ matrix.mode }} | tee perf/results/j_normperf/${{ matrix.source_text }}/${{ matrix.perf }}/output.txt
           cat perf/results/j_normperf/${{ matrix.source_text }}/${{ matrix.perf }}/output.txt
 
       - name: Store performance test results
@@ -598,15 +600,14 @@ jobs:
           git restore --staged tools/multi/proj/icu4cscan/old-xmls.tar.bz2;
           git restore tools/multi/proj/icu4cscan/old-xmls.tar.bz2;
           cd icu4j;
-          ant;
-          ant perf-tests;
+          mvn install -DskipITs -DskipTests;
           cd perf-tests;
           mkdir -p perf/results/j_converterperf/${{ matrix.source_text }}/${{ matrix.test_enc }}/${{ matrix.perf }};
           # Delay execution by random number of seconds. Spreading execution of multiple
           # tests over 180 secs. minimizes the possibility of push conflicts when storing
           # tests results in the data branch.
           sleep $(($RANDOM % 180));
-          java -cp ./out/bin:../tools/misc/out/bin/:../icu4j.jar:../icu4j-charset.jar com.ibm.icu.dev.test.perf.ConverterPerformanceTest ${{ matrix.perf }} -a -t 2 -p 4 -f $DATA_FILE_PATH/${{ matrix.source_text }}.txt -e UTF-8 -T ${{ matrix.test_enc }} | tee perf/results/j_converterperf/${{ matrix.source_text }}/${{ matrix.test_enc }}/${{ matrix.perf }}/output.txt
+          java -cp ../tools/misc/target/:../../icu4j/main/icu4j/target/:../../icu4j/main/charset/target/ com.ibm.icu.dev.test.perf.ConverterPerformanceTest ${{ matrix.perf }} -a -t 2 -p 4 -f $DATA_FILE_PATH/${{ matrix.source_text }}.txt -e UTF-8 -T ${{ matrix.test_enc }} | tee perf/results/j_converterperf/${{ matrix.source_text }}/${{ matrix.test_enc }}/${{ matrix.perf }}/output.txt
 
       - name: Store performance test results
         uses: gregtatum/github-action-benchmark@d3f06f738e9612988d575db23fae5ca0008d3d12
@@ -676,15 +677,14 @@ jobs:
           git restore --staged tools/multi/proj/icu4cscan/old-xmls.tar.bz2
           git restore tools/multi/proj/icu4cscan/old-xmls.tar.bz2
           cd icu4j;
-          ant;
-          ant perf-tests;
+          mvn install -DskipITs -DskipTests;
           cd perf-tests;
           mkdir -p perf/results/j_dateformatperf/${{ matrix.locale }}/${{ matrix.perf }}/${{ env.DDIR }};
           # Delay execution by random number of seconds. Spreading execution of multiple
           # tests over 180 secs. minimizes the possibility of push conflicts when storing
           # tests results in the data branch.
           sleep $(($RANDOM % 180));
-          java -cp ./out/bin:../tools/misc/out/bin/:../icu4j.jar com.ibm.icu.dev.test.perf.DateFormatPerformanceTest ${{ matrix.perf }} -a -t 2 -p 4 -L ${{ matrix.locale }} ${{ env.PARM }} -r 1 | tee perf/results/j_dateformatperf/${{ matrix.locale }}/${{ matrix.perf }}/${{ env.DDIR }}/output.txt
+          java -cp ../tools/misc/target/:../../icu4j/main/icu4j/target/ com.ibm.icu.dev.test.perf.DateFormatPerformanceTest ${{ matrix.perf }} -a -t 2 -p 4 -L ${{ matrix.locale }} ${{ env.PARM }} -r 1 | tee perf/results/j_dateformatperf/${{ matrix.locale }}/${{ matrix.perf }}/${{ env.DDIR }}/output.txt
 
       - name: Store performance test results
         uses: gregtatum/github-action-benchmark@d3f06f738e9612988d575db23fae5ca0008d3d12
diff --git a/.github/workflows/maven.yaml b/.github/workflows/maven.yaml
index f6eb58e201c..716f3f0fe8b 100644
--- a/.github/workflows/maven.yaml
+++ b/.github/workflows/maven.yaml
@@ -2,6 +2,12 @@ name: Publish icu4j.jar/utilities.jar to GH Maven
 on:
   release:
     types: [created]
+  workflow_dispatch:
+    # To trigger the Env Test workflow manually, follow the instructions in
+    # https://docs.github.com/en/actions/managing-workflow-runs/manually-running-a-workflow
+
+env:
+  MAVEN_ARGS: '--show-version --no-transfer-progress'
 
 permissions:
   contents: read