Why can't I use TortoiseMerge as my git merge tool on Windows?

If you have the latest git, run this command line once:

git config merge.tool tortoisemerge

Important: Do not add a .exe extension to the command.

If that fails, or if you want to add a different merge tool that git doesn't know about, do this:

Open one of the following in an editor:

• 64-bit git: C:\Program Files\Git\mingw64\share\git-gui\lib\mergetool.tcl
• 32-bit git: C:\Program Files (x86)\Git\share\git-gui\lib\mergetool.tcl

Add something like this to mergetool.tcl:

tortoisemerge {    set cmdline [list TortoiseMerge.exe -base:"$BASE" -mine:"$LOCAL" -theirs:"$REMOTE" -merged:"$MERGED"]}

Put the new tortoisemerge entry above this other code:

default {        error_popup [mc "Unsupported merge tool '%s'" $tool]        return}

Bonus example:

To use SourceGear diffmerge, add this to mergetool.tcl:

diffmerge {    set cmdline [list "C:/Program Files (x86)/SourceGear/DiffMerge/DiffMerge.exe" --merge --result=$MERGED $LOCAL $BASE $REMOTE]}

Try this:

[merge]tool = tortoise[mergetool "tortoise"]cmd = "TortoiseMerge.exe" -base:"$BASE" -theirs:"$REMOTE" -mine:"$LOCAL" -merged:"$MERGED"

Source: http://programmersunlimited.wordpress.com/2010/07/01/getting-git-to-use-tortoisemerge/

For the case that I was working on, the mergetool was already set to tortoisemerge, but it could not find it.

Providing a fully qualified location worked in Windows:

git config --global mergetool.tortoisemerge.cmd "\"C:\\Program Files\\TortoiseGit\\bin\\TortoiseGitMerge.exe\" -base:\"$BASE\" -mine:\"$LOCAL\" -theirs:\"$REMOTE\" -merged:\"$MERGED\""