Lawrence O’Donnell is, even by the standards of MSNBC anchors, a busy guy. The host of “The Last Word” (which airs nightly at 10 p.m.), O’Donnell has long enjoyed a sideline career as an actor, appearing in the television series “Big Love,” “Homeland,” and “Monk,” among others; he also served as an executive producer for “The West Wing.”

The news anchor is about to hit movie screens in perhaps his highest-profile cameo yet, as a news anchor (for a generic news network, explicitly not MSNBC) in the action drama “Olympus Has Fallen,” which depicts an attack by North Koreans upon the White House and features Aaron Eckhart and potential Senate candidate Ashley Judd as the president and first lady. We spoke to O’Donnell about his unusual career, why Jim Lehrer would never do what he does, and his future in Hollywood.

Why do you say yes when offered films? The director of “Olympus Has Fallen” told us that he’d reached out to many news anchors, including CNN’s Don Lemon, and only you were able to do it.

Because I miss show business so desperately that I will do anything short of pornography at this point to hang around sets and have fun.

Sets are really fun workplaces and everyone there is creative and energetic. These are the most creative electricians in the world. They’re not the electricians who come to your house. They’re the most creative carpenters, the most creative carpenters, writers, directors, directors of photography: there’s a great spirit to a film set that is unique in American workplaces by far. And it is the most fun I’ve had in my professional life.

Do you try to import some of that moviemaking magic onto the set of your nightly show?

The comparison is tragic for me. What I’d love to have is a crawl at the bottom of the screen, reading: “You are watching an unrehearsed first draft.”

Both of those things are just horrendous notions to me: To put something onscreen unrehearsed is just madness. To expose a first draft to anyone’s ears other than your own is indecent. And we combine those two sins against good writing every night, and throw it out there. And so every show we do offends my artistic sensibilities in some ways.

It’s the cruelest deadline I’ve ever been exposed to. All writers are forced to live within deadlines, and deadlines determine how good they can be. If you have five weeks to write an episode of television or seven months to write a movie or several years to write a book, each of those things is going to be better than a live television show. Luckily, the audience is apparently understanding, and they forgive much.

What compelled you to say yes to this film — which has a pretty shocking, unbelievable plot?

The part of that script that appealed to me were my lines. That’s all I know about that script. I haven’t seen another page of that script. I only know what happens based only on the lines I read. It might be the only time I did a project like that where I did nothing but read my lines. It’s a movie I couldn’t possibly conceive of in my wildest dreams. I’m too grounded in reality. That’s what the creative members of the Writers’ Guild are for.

There’s another one coming along with pretty much the same concept, with Channing Tatum. [“White House Down,” another film about a coup in the White House, is set to be released this summer.] I got a call last week, asking, Would I do same thing in that movie? Would I do a newscaster thing about the White House being taken over? I said, Oh yeah, sure.

The day before I was going to do it, they discovered [I was in “Olympus Has Fallen”]. I’d forgotten about the other movie. It was filmed months ago. I would have alerted them to it. But maybe it’d be kind of funny — this is the guy who pretends the White House has been taken over.

Do you worry appearing on television and in films might dilute your authority?

Luckily, I have no authority to lose, so there’s no risk. At “The West Wing,” I cast newscasters, and when you put out a casting call for actors, half of the people who come in are real local L.A. newscasters. Each time, I ended up hiring one of them, because they’re better at it. Big surprise! A newscaster is better at playing a newscaster than an actor is. The truth is that most people who see this movie have no idea. They haven’t seen [“Last Word”] before. You have to understand how tiny the audiences are are for cable news. Maybe one-seventh of the people who see Brian Williams’s show see me. You could put me in movies, and most people wouldn’t know who i am.