In the 1990s she played feisty prison boss Helen Hewitt in Lynda La Plante's The Governor, which paved the way for DS Amy Foster in 2007's BBC mini-series Five Days.
"I've been tall all my life," the Oscar-nominated actress jokes.
"But I think it probably helps from the perspective of the writers, because if you're tall and you have a voice like an old transvestite then you automatically have presence."
Now Janet, 47, is set to revisit DS Foster alongside her partner DSI Iain Barclay, played by Hugh Bonneville, in new ITV1 drama Hunter.
"We had such a good time on Five Days - it was beautifully written - so it was fun to revisit such great characters," she says over coffee at a private London club.
"Hugh and I are mates anyway and we have a lovely time working together, so it seemed like the perfect job."
Hunter takes place some six months after Five Days ended and sees Barclay persuade Foster to come out of early retirement to work on one more case.
"Barclay and Foster are both workaholics, they understand each other very well and when she takes early retirement, she's bored out of her brain, she can't cope with it and she can't wait to come back to work."
The detectives work best when they're sparking off each other because they have complementary attributes - she's street-smart and he's more intuitive.
"I love the fact that their relationship is mates, I don't think you see that on TV between a woman and a man and I like that a lot," says Janet.
Barclay and Foster's close bond must have been helped by the fact that Janet and Hugh were friends in real life, but she says otherwise.
"When you act together, that's completely different from knowing each other in social circumstances. But once we'd worked on Five Days, we had similar ideas and ways of looking at scenes and we got on really well as actors.
"Given the fact we do an awful lot of scenes together, it was good to have a nice working relationship," she adds, with a smile.
Five Days was a five-part ensemble drama dealing with the disappearance of a mother and her two children, whereas Hunter is just two episodes focusing on the dynamics between Barclay, Foster and their inexperienced team.
The investigation centres on the motives of extremists who have kidnapped two children from very different backgrounds. They promise to release them only if their demands are met.
But when Barclay and his unreliable team make no progress in finding the children, he calls in his former deputy Foster to whip them into shape.
"I like playing this sassy workaholic who's come up through the ranks," says Janet.
"She doesn't take any nonsense and she's tough like a lot of women coppers have to be, they've come up through a lot of misogynistic attitude and she can give that back in spades."
To prepare for their roles Janet, Hugh and the supporting cast met a retired detective, who had worked on child cases and talked them through police procedure.
Filming made Janet realise how tough it is to be a police officer and work on such sensitive cases in real life.
"One of the things that was quite humbling about doing this, was that you go home at the end of the day and know you're doing a drama and they're doing the real stuff.
"If I were Foster, if we were really this team, I would be going home, thinking 'I can't sleep because I don't know where those two kids are' and it's down to us.
"I think there's a huge amount of alcoholism in the police force and broken marriages and they find it very hard," Janet continues.
"They're dealing with such difficult subjects, so to go home and switch off from it is very hard and has a huge effect on their private lives."
As an actress, the hardest thing Janet had to cope with was learning her lines.
"On the way home, you're thinking, 's***, what do I have to say tomorrow?' and you're working on your lines, so it's very different."
Auburn-haired Janet was born in Newcastle and trained at RADA before starting her acting career on the stage.
Her big screen debut came in 1986's Half Moon Street, based on a novel by Paul Theroux, and was followed up with Wuthering Heights and a string of TV roles.
In the 90s she returned to the West End stage and won critical acclaim for her portrayal of Nora in Ibsen's The Dolls House, which transferred to Broadway.
She won an Oscar nomination and a Golden Globe for Best Actress for the 1999 comedy film Tumbleweeds, in which she played an American woman who constantly moves town with her 12-year-old daughter.
She's returning to the big screen later this year in Into The Storm, as Winston Churchill's wife Clemmie. Janet's also heading back to Broadway to play Mary, Queen Of Scots in Mary Stuart
I find it hard not to draw comparisons between Janet and her fellow actress Helen Mirren - they've both appeared as feisty TV detectives and Lynda La Plante creations, and are forging successful careers as older actresses.
"How can you not dote on Helen Mirren?" says Janet.
"I watched all of the Prime Suspects, I didn't base Foster on her, but in terms of having great roles for grown-up cops, I think it's pretty cool.
"There aren't many great roles for grown-up women on television and to play a grown-up woman, who's not sort of anybody's sidekick, who's not a mother, she's a workaholic, tough cookie. I love that, it's really good fun and... I'm much taller than Helen Mirren."
JANET MCTEER - EXTRA TIME
Janet was born in 1961 in Newcastle-Upon-Tyne and started her career in acting on stage at the Royal Exchange Theatre.
She was spotted for the role of the nomadic mother in Tumbleweeds, by filmmaker Gavin O'Connor when she was being interviewed on a US chatshow.
Last year in the Queen's Birthday Honours, she was appointed Officer of the Order of the British Empire (OBE) for her services to acting.
For her next film project, Janet's off to the Isle of Mull to make The Sea Change.
"I play Phyllis, the mother of Nathalie Press, who opens the film by saying, 'When I was 29, I decided to kill my mother'. I'll leave the rest to you!"
Janet would have loved to appear in The West Wing, as CJ Cregg's sister.
Hunter started on BBC One on Sunday January 18.