Love, which has received critical raves. In addition the HBO series Togetherness, which he and his brother, Jay Duplass, have created and written, is set for a January premiere.
In the meantime, though, his series The League will return for a sixth season on FXX, debuting Wednesday. The semi-scripted series revolves around a fantasy football league.
"It's hard to say what's so appealing about the show," Duplass says, speaking by telephone from The League's Chicago set on a rainy afternoon. "It's technically about fantasy football, but it's not really about that in the long haul.
"We're so brutally honest and despicable as friends as characters on this show," he says. "I wish I could speak that honestly to friends in real life — and still be friends."
The new season, Duplass says, will feature numerous cameos by NFL players.
"There will be terrible fashion sense," he continues, "and I will be dating women who are younger than me. That about sums it up."
The show is shot in Chicago, so it's no surprise that its N.F.L. guest stars are heavily drawn from the Chicago Bears, then and now. Current Bears quarterback Jay Cutler made a cameo last year, to Duplass's delight.
"We even had Jay Cutler's baby on the show, who was dubbed `the Cutlet,'" he says. "The Cutlet was better as an actor than all of us. Before the age of reason kicks in, you always find the best actors. And the Cutlet didn't say, `Get that camera out of my face.'
"Meanwhile Jay was great," Duplass says. "His lovely wife [reality star Kristin Cavallari] wanted him to do the show, and he did it."
His favorite NFL star appearance was another Bears quarterback, one of the team's best ever.
"We had Jim McMahon on the show," Duplass says. "He was the leader of the 1985 Bears, and that was the most starstruck experience for all of us. I had to contain myself not to ask him to do the Super Bowl Shuffle.
"He's a rock star," the actor continues. "That team took the NFL by storm. There was even one season where Walter Payton played quarterback for four games when McMahon got hurt. `The Fridge' was breaking all the rules. Those guys were badasses to me."
Did McMahon do the Super Bowl Shuffle?
"No, I didn't ask," Duplass says. "You need to be respectful. I didn't want Jim to think that I was a total idiot."
In his new film, The One I Love, Duplass and Elisabeth Moss of Mad Men play a couple whose relationship is on the rocks. They decide to entrust their marriage to an unorthodox therapist (Ted Danson) who has them relocate to an isolated country estate where everything changes.
"The film allows us to explore why it is that, when you first start to date someone, you present this shinier version of yourself who is into museums and books and is so [amazingly] sensitive," Duplass says. "Then the real person comes out and the other person says, `Whoa, that's who you are now?'"
He himself is no exception, says the actor, who has been married for 12 years to actress Katie Aselton, his co-star Jenny in The League and several Duplass brothers films.
"I'm guilty of doing this too," Duplass admits. "When we were first dating, I pretended to read this book or that book. Later she asked, `What did you think of the resolve of that book?' I could only say, `Uh ... ‘"
Women do the same thing, he adds, for example by pretending to love sports.
"What girl doesn't want to be the guy's girl when you first start dating someone?," he says.
"Dating is literally like you're watching a National Geographic special where the animal puts on his or her shiny coat," Duplass concludes. "Then later you take off the coat and see all the warts."
He had never worked with Moss before, but says that he found it a treat.
"Elisabeth is really great," Duplass says. "She does that wonderful work in Mad Men, where she's so measured and a real guy's girl who is light and airy. We needed an actress in this who could play all of those shades."
After growing up in New Orleans, Mark and Jay Duplass broke into filmmaking as the writers and directors of The Puffy Chair (2005), a picaresque road movie which scored a hit at the Sundance Film Festival and was picked up by Roadside Attractions. They followed with Baghead (2008), Cyrus (2010), Jeff, Who Lives at Home (2011), and The Do-Deca-Pentathlon (2012).
Meanwhile Duplass has built a parallel career as an actor, appearing in such films as Greenberg (2010), Safety Not Guaranteed (2012), Darling Companion (2012), People Like Us (2012), Zero Dark Thirty (2012), Parkland (2013), and Tammy. Besides his work on The League, he also plays Brendan on Fox's The Mindy Project, starring Mindy Kaling.
His next big project is Togetherness, which he and Jay wrote and directed and in which he also stars. The HBO show is about two couples who live together, with Abby Ryder Fortson, Melanie Lynskey, Amanda Peet, and Steve Zissis co-starring.
"It's a couples show," Duplass says. "Everyone on the show is married and dealing with kids. My couple faces the fact that our friends are literally living on our couch.
"At its core, it's a dramatic comedy," he continues. "It's about the universal quest to try to be a good spouse, a good parent and a good friend, and even a good child, while still trying to achieve your personal dreams in life. I've found that, in real life, all of those things can be at odds with each other at times."
The father of a 6-year-old and a 2-year-old, Duplass speaks — and writes — from experience.
"Just like the people on the show, I'm going for the American dream and falling short somewhere every single day," he says with a wry laugh. "I've found that it's really hard, maybe impossible, to fit my work, my wife and my kids, plus a few very good friends, into one day.
"You just feel like you're always missing something every single day," Duplass says, "but then you get up and do it over and over again. You try to get it right.
"I guess that's life in your 30s."