m2e plugin in version >= 1.6 does not support Maven 2. If you want to install m2e plugin in Eclipse Mars with m2e 1.6 already installed (see row "Maven Integration for Eclipse" at. https://eclipse.org/downloads/compare.php?release=mars) you should:

1. download Eclipse Luna Package with "Maven Integration for Eclipse" installed;

2. copy all jars and directories from

   ${eclipse_luna}\plugins 

starting with org.eclipse.m2e prefix to

 ${eclipse_mars}\plugins; 

3. in

   ${eclipse_mars}\configuration\org.eclipse.equinox.simpleconfigurator\bundles.info 

remove all lines starting with org.eclipse.m2e prefix and copy-paste all lines starting with org.eclipse.m2e from

 ${eclipse_luna}\configuration\org.eclipse.equinox.simpleconfigurator\bundles.info 

Remember not to update "Maven Integration for Eclipse" feature, because it will probably overwrite above changes.

m2e plugin in version >= 1.6 does not support Maven 2. If you want to install m2e plugin 1.5.x in Eclipse Mars with m2e 1.6 already installed (see row "Maven Integration for Eclipse" at. https://eclipse.org/downloads/compare.php?release=mars) you should:

1. download Eclipse Luna Package with "Maven Integration for Eclipse" installed;

2. copy all jars and directories from

   ${eclipse_luna}\plugins 

starting with org.eclipse.m2e prefix to

 ${eclipse_mars}\plugins; 

3. in

   ${eclipse_mars}\configuration\org.eclipse.equinox.simpleconfigurator\bundles.info 

remove all lines starting with org.eclipse.m2e prefix and copy-paste all lines starting with org.eclipse.m2e from

 ${eclipse_luna}\configuration\org.eclipse.equinox.simpleconfigurator\bundles.info 

Remember not to update "Maven Integration for Eclipse" feature, because it will probably overwrite above changes.