Mark Duplass has one of the most unique careers going in films today.

He’s teamed up with his brother Jay to co-write and direct a string of critically acclaimed films – including the recent “Jeff, Who Lives at Home” and “Cyrus,” which was my favorite film of 2010 – that are at the forefront of the super-low-budget, dialogue-driven, “mumblecore” indie-movie wave.

At the same time, Duplass is branching off on his own as an actor, taking the lead in other indie films like “Humpday” before  a current string of supporting roles in quirky ensemble casts with major stars.

His latest acting role comes in director Lawrence Kasdan’s first independent film, “Darling Companion,” in theaters now but opening wide April 27. Duplass is surrounded by high-class vets like Diane Keaton and Kevin Kline in a tale of an older couple re-examining their marriage after their dog runs away. Speaking at a press junket at the Beverly Hills Four Seasons, Duplass not only commented on the challenge of acting against some of the modern era’s biggest stars, but also the process involved in creating his unique films, and the many deeper meanings of “Jeff.”

BH: So you’re making a real leap into bigger films as an actor.

MD: I was honestly just excited to be around them and go to Park City [Utah] for six weeks on the shoot and share a life experience with them, which is almost as important as the piece of art itself. I was intimidated at first, but in the case of Keaton, she’s so vital and struggling to figure it out even as long as she’s been doing it. They set me at ease.

BH: So how did you decide to branch into acting, when Jay doesn’t? 

MD: I have more of a work appetite than Jay does, so honestly when Jay and I are not working together, acting is really fun and fascinating as well. Jay and I are writers as well, so that is a nice balance. We’re still united on the film front, and acting is what I like to do with the rest of my time.

BH: “Jeff Who Lives at Home” marked a big step forward for you guys in terms of how much you broadened out the story into the real world, with car crashes and jumping off bridges. Are things going to keep getting bigger with yours and Jay’s films? 

MD: You’d be surprised how much the budget on “Jeff” was. Not much more than “Cyrus.” We want to make them modestly so they don’t have to make a ton of profit to keep going. Every film has its appropriate budget level. If we want something really quirky, we’ll do a real small budget. If we think of something in space, screw it – ask for more money. I haven’t found any ideas that attract us personally and keep us involved as directors. We are still talking about $20,000 movies, so we won’t abandon our micro roots.

BH: “Jeff” had a very strong spiritual side, depicting this seemingly lost soul of a stoner and gradually giving him real purpose and meaning in the world. How did you manage to get that into a movie put out by Hollywood?

MD: We were raised Catholic. I’m not sure if it had an effect on the film or not in terms of Jeff’s belief in the universe and its plan for him. The most important thing to realize about the movie is that characters who believe deeply are compelling to watch. I hadn’t made a movie like that yet. We loved the documentary “American Movie” and the original “Rocky” and these lovable losers with giant dreams and very little life skills to achieve them and we love them anyway. You think you know Jeff as the stoner who lives in mom’s basement, but he’s not a slacker and has the utmost integrity. He’s suspended chasing life because he thinks the universe will deliver it to him.

BH: So what was it like working with Larry Kasdan, who’s done some really meaningful films himself? 

MD: Some of his movies are my favorite of all time. “Accidental Tourist” when I was 10 years old and man, how that affected me. I was in awe of the guy, such an incredible partnership. I’m not an easy actor to work with all the time. I’m not a pushover and have to believe what I’m doing, and Larry had a vision for what the film should be. I’d overspeak it and he’d reduce it to something concise and clear and we’d go with that. I have the utmost respect for his process.

BH: And so what’s next for you and Jay?

MD: We’re writing five different movies right now – some for studios, some especially for us, and they range from $20,000 to $20 million budgets. I’m producing others, and I’ll be acting in the FX series “The League.” Maintaining our ethic of one foot in the Hollywood system and the other in the microbudget sphere where nobody can mess with us.