Marc Masterson is exiting his post as a.d. at the Actors Theater of Louisville, Ky., to take up the reins at Costa Mesa’s South Coast Repertory.

Masterson has spent 11 seasons in the top post at ATL, the theater that programs and produces the Humana Festival New American Plays.

Move comes soon after the announcement that SCR’s co-founders, Martin Benson and David Emmes, will step down from their leadership gigs but continue on with the org as founding directors. Both in their 70s, the duo founded SCR in 1964.

Like ATL, SCR has gained a rep for its development of new plays, with activities including the annual Pacific Playwrights Festival. Richard Greenberg, Amy Freed and Craig Lucas are among the scribes to have had preems at the theater.

Under Masterson’s tenure at ATL, Humana offerings that have gone on to be seen in Gotham include recent Off Broadway offerings “Becky Shaw” and “The Scene.” Some 85% of Masterson-programmed Humana shows have been picked up for future productions, according to the theater.

Masterson is expected to begin his gig at SCR part-time after this year’s Humana Fest (running Feb. 27-April 3) and move completely into his new post by Sept. 1. Benson and Emmes’ responsibilities at the theater will include directing one show per year as well as scouting for new work.

A search for Masterson’s replacement at ATL will begin soon.