Jim Gaffigan and Olivia Thirlby have joined the cast of Chappaquiddick, the indie drama being directed by John Curran from Taylor Allen and Andrew Logan’s Black List script. The Gaffigan and Thirlby join Jason Clarke, who plays Ted Kennedy, and Kate Mara, who plays Mary Jo Kopechne, in the based-on-real-life tragedy tale. Ed Helms and Bruce Dern co-star. Shooting is now set to start September 7 in Boston.

WME serves as the film’s North American sales agent, and Sierra/Affinity has come on board to rep international sales.

Chappaquiddick of course revolves around the tragic car accident that took the life of Kopechne when Sen. Kenned was at the wheel in the summer of 1969. After driving off a bridge, Kennedy escaped the car and left the scene of the accident, leaving the 28 year-old Kopechne to drown, and he didn’t report the accident for nine hours. Gaffigan will play District Attorney Paul Markham, and Thirlby will play a member of the so-called “boiler room girls,” a group of single women who attended the party on Chappaquiddick before the accident and worked on Bobby Kennedy’s 1968 Presidential campaign.

Apex Entertainment’s Mark Ciardi and Campbell McInnes are producing and Apex is financing. DMG’s Chris Cowles and Chris Fenton are executive producing with Taylor Allen and Logan.

Gaffigan is repped by UTA and Brillstein Entertainment Partners. Thirlby is repped by CAA, 3 Arts and Hansen Jacobson.