The announcement was first revealed by Deadline Friday and confirmed by the actor on social media shortly thereafter.
"The galaxy far far away has had almost as much influence as the one I live in, so I am delighted to be involved," Monaghan said in Deadline's report regarding joining the Lucasfilm and Disney movie.
Monaghan played rocker Charlie on the ABC series that debuted in 2004, featuring most prominently during the show's first three seasons while making appearances throughout the latter half of the show's six-season run.
Before that, Monaghan played Merry in the first three Lord of the Rings films that premiered starting in 2001 through to 2003.
Former Lost costar Evangeline Lilly has a similar track record, starring as Kate in Lost before starring in the three movies based on The Hobbit as Tauriel and most recently in Marvel/Disney's Ant-Man as well as Ant-Man and the Wasp.
Lilly recently said that she has asked Abrams if she could join the Star Wars too, asking the director if she could somehow take on the role of Leia Organa.