In it, the 53-year-old stars with Anna Faris as a dysfunctional mother-daughter duo in recovery from their respective alcohol and drug addictions.
Although addiction might seem curious subject matter for mainstream comedic fare, the show is created by veteran sitcom producer-writer-director Chuck Lorre, who has never been afraid of controversy.
Says Janney: "There are a lot of people in recovery and I've had a lot of people in my life who have been in recovery. Some have made it; some have not. When I read this script I realised that this is a subject dear to my heart. I love that these two women are trying to be better people and trying so hard to be sober.
"And while there's nothing funny about recovery, sobriety or addiction ... we deal with a lot of issues but we don't make fun of them. We own them and we are in them," she explains.
"If you remember the Roseanne show [another of Lorre's creations], the best moments were the darker ones, those are the moments that endure; that's why it works.
"When we're going through something painful, we have a tendency to laugh at ourselves."
Janney is in the enviable position of having concurrent roles in drama and comedy.
She says, "I like a healthy mix of both. Masters of Sex is dramatic but there's also humour in it, and I love those scenes.
"Likewise, in Mom I'm allowed to be very emotional. They are very different muscles I'm using because they're not similar characters at all.
"But I have to be honest, I was a little worried about being able to do both. In the beginning when I was on the set of Mom I'd think, 'Gosh, I have to shoot this comedy while I'm in the middle of this period piece about this woman who's never had an orgasm before, and I'm about to play a woman who has 25 a day," she laughs.
"I'm very grateful for my theatre training because you learn how to do different styles, and that experience has served me well in going back and forth from Masters and Mom."
Janney was attracted to the role of Bonnie Plunkett in part because it was tailor-made for her.
'I think Bonnie probably sticks with me a little bit. Just her sense of fun, she shoots from the hip, and she's got a thicker skin than I do, and that's kind of fun to take that on and take that home with me. I definitely need a thicker skin.
"I'm enjoying it immensely because they're writing to my physical specifics. I'm a very physical person and I grew up watching The Carol Burnett Show so that's where I got that from. I took ballet classes and figure skating and I'm very aware of my body. I like to use it in a comic way. It's a skill of mine, and I love it."
Being tall - Janney is 1.83m - can't always be an advantage for a woman in Hollywood, especially considering that many male counterparts veer towards the diminutive side.
"In the beginning of my career my height really hurt me. I had to play 40-year-old women when I was 20, and then there was a moment when I couldn't get cast in the roles I was right for because I was too tall. I couldn't play the ingenue and I just couldn't get any work. In fact, I almost quit acting, but then as I got older being tall started to work for me," she laughs.
"So now it's an asset, as long as I don't wear heels."
While that height has helped get her cast as various mothers in funny movies like Juno and last year's The Way Way Back, working on a sitcom in front of a studio audience has greater personal rewards.
"I have to say that making people laugh is an addiction and it fills me with joy.
"To hear the audience laugh hysterically, there's no greater feeling, other than when Chuck Lorre laughs.
"When you make him laugh, its like, 'Ah, job security."'
Lowdown
Who: Allison Janney
What: Mom, the new sitcom from Chuck Lorre, creator of Two and a Half Men and The Big Bang Theory, among others
When: TV2 Wednesday February 12, 7.30pm
