You might know busy actor Liev Schreiber from his Emmy-nominated starring role on Showtime’s “Ray Donovan” — but what you might not know know is that he has a thriving second career as a voiceover artist.

Schreiber has lent his pipes to dozens of documentaries and commercials, and, since 1995, has been the main voice of HBO Sports documentaries including “Countdown,” “24/7” and “Hard Knocks.” “Along with his incredible voice, he brings a passion for storytelling to every project he narrates for us,” says HBO Sports VP/senior producer Bentley Weiner. Schreiber’s dulcet tones can also be heard narrating dozens of documentaries on networks including PBS, National Geographic, Smithsonian Channel and History Channel.

“Liev was perfect — his talent and skill as a dramatic actor adds a natural rhythm that drives the narrative and creates peaks and valleys,” says Joy Galane, VP of Post Production, Smithsonian Channel, of Schreiber’s work on the network’s documentary “America in Color.” “His voice lends itself to a rich delivery adding a compelling, even mesmerizing quality that draws the viewer in.”

Schreiber, 49, answered a few questions from The Post about his voiceover career.

Did you ever think your voiceover career would work out this way?

When I first got into acting, I really hoped and prayed that one day I would be able to get into voiceover. It seemed like a great gig — you sit in a room, nobody sees you, you read [your lines] and you go home. I guess one of the things that probably led to me staying in the business were my low expectations. I have low expectations for everything.

I think one of the most exciting moments for me was when a guy named David Espar from WGBH made [the documentary] “Rock and Roll” [in 1995]. He either saw me, or someone he knew saw me in a Shakespeare play or heard my voice. I guess thought I was 40 or 50, and he was really shocked when he found out I was 25 or 26 and he was brave enough to take a risk on me. With voiceover jobs I get a lot of credit for stuff I have very little to do with. [Voiceover] is usually the last kind of creative impulse. What I’m really doing is reading other people’s scripts.

Is voiceover work more difficult that acting on-screen?

You’re not in control the same way you are when you’re on-camera. It’s a much bigger responsibility to hold the narrative, for driving its credibility. In a [TV or movie] cast, that’s sort of spread out among the players. The narrator has a real responsibility for the tone. I got discovered by HBO Sports and that was an incredible training ground for me. They basically gave me my start. [Former HBO Sports president] Ross Greenburg heard me on “Rock and Roll” and brought me into HBO.

Do you use different deliveries for different voiceover genres?

My mom says she doesn’t recognize my voice. I naturally have a kind of more ethnic New York sound when I’m doing sports [documentaries]. I’m a fan of [NFL Films voiceover legend] John Facenda: “As they galloped across the field in Minnesota …” that kind of epic poetry. I’m a classically trained actor, so of course that appeals to me. When I first started, that kind of more classical delivery took me out of the ethnicity, which might have been a good thing. The reality of our profession is that we’re the instrument of the writer, and I think that approach lends itself to voiceover: parsing the text and understanding the writer’s intention and ambition. It’s your job to articulate those ideas.

Any favorite voiceover projects over the years?

One the best things I ever worked on was “Rock and Roll.” And HBO has been the centrifuge of my career and has been such incredible experience for me. I love everything they’ve done, in particular “Magic & Bird,” which went into the rivalry between Magic Johnson and Larry Bird. That particular documentary knocked my socks off.