The MercurialEclipse plugin brings support for Mercurial to Eclipse.
To install it, go to Help -> Install New Software and add the URL: http://mercurialeclipse.eclipselabs.org.codespot.com/hg.wiki/update_site/stable
I usually manage Mercurial from the shell. To enable Mercurial support for an existing project that is placed in a Mercurial repository is easy. Click on the project in Project Explorer, choose Team -> Share Project. Click on Mercurial and click Next. Choose Use existing repository in parent directory. Check if the path in Selected Repository is correct. Click Finish.
When Mercurial support is working, you can see that the directories and files shown in Project Explorer have icon overlays that indicate their modified or committed status.
Almost all the Mercurial operations can be accessed by clicking on the project or file in Project Explorer and choosing Team. Its a bit confusing that this is not named something appropriate like Mercurial or Hg or even version control.
To view the history log of the project, choose Team -> Show History. The History window is shown at the bottom of Eclipse. To enable viewing the graph of changes, click on the Show Parent History button in this window.
To view the uncommitted changes of a file as a side-by-side diff with its parent revision, click on the file and choose Compare With.
Other basic operations of this plugin are described in this page.
Tried with: MercurialEclipse 2.1.0, Eclipse Luna 4.4.1 and Ubuntu 14.04