While playing Story Mode In Episode 1, Chapter 6 "Darth Maul", make sure you are using the Qui-Gon character rather than Obi-Wan. When you deplete the final heart in Darth Maul's health bar, the Achievement will unlock.
The Achievement works the same was as the similar Achievements in LEGO Indiana Jones; you can also choose Qui-Gon and Darth Maul in Free Play once you've unlocked him, and simply destroy your teammate. This was confirmed by
SneeringMeerkat