1. Launch External Merge Tool Sourcetree
2. Launch External Merge Tool Sourcetree Mac

This helped me too as I am a windows sourcetree user. Another problem I had was in the sourcetree options. Under the 'Diff' tab options there are 2 settings, one for 'External Diff Tool' and one for 'Merge Tool'. I assumed I had to set the 'External Diff Tool' because it had the word 'External' in it, but it was actually the 'Merge. To resolve a conflict, right click on a conflicted file in SourceTree, Resolve Conflicts Launch External Merge Tool, resolve conflicts in Visual Studio and finish by clicking Accept Merge. That’s all there is to it. Now if you, like me, like Visual Studio’s merge tool then you’re literally 5 minutes away from linking it to SourceTree.

Using TortoiseDiff and TortoiseMerge in Atlassian SourceTree

I’m using SourceTree along with TortoiseMerge/Diff, which is very easy and convenient diff/merge tool. But, because it isn’t that easy and convenient to install and configure both tools, I wrote this simple memo-post to have check-list for future reference in one place.

Launch External Merge Tool Sourcetree

Steps.

1. Get standalone version of TortoiseMerge/Diff (quite old, since it doesn’t ship standalone since version 1.6.7 of TortosieSVN, that is since July 2011). Links and details in this answer.

2. Unzip TortoiseIDiff.exe and TortoiseMerge.exe to any folder (c:Program Files (x86)AtlassianSourceTreeextras in my case).

3. In SourceTree open Tools > Options > Diff > External Diff / Merge. Select TortoiseMerge in both dropdown lists.

4. Hit OK and point SourceTree to your location of TortoiseIDiff.exe and TortoiseMerge.exe.

After that, you can select Resolve Conflicts > Launch External Merge Tool from context menu on each conflicted file in your local repository. This will open up TortoiseMerge, where you can easily deal with all the conflicts, you have. Once finished, simply close TortoiseMerge (you don’t even need to save changes, this will probably be done automatically) and after few seconds SourceTree should handle that gracefully.

The only problem is, that it automatically creates backup copy, even though proper option is unchecked.

There is an alternate solution to this problem, which uses KDiff3 instead of TortoiseDiff / TortoiseMerge.

Launch External Merge Tool Sourcetree Mac

Source of this article: Stack Overflow.