After working in the local biscuit factory, she racked up starring roles and screenwriting credits on some of Britain's biggest TV soap operas.
Then real-life tragedy struck in her hometown.
In the by-election that followed in the northern England constituency of Batley and Spen, Brabin was effectively handed Cox's seat; none of the major political parties fielded candidates, the only people who stood against her were from far-right fringe parties. They were soundly defeated.
"I didn't yearn for a political career, but politics chose me," the 56-year-old, mother-of-two says.
But seven months after she took her place in Westminster, Brabin is campaigning for re-election, after Prime Minister Theresa May called a snap nationwide vote on June 8. The Batley and Spen seat has been held by Labour since 1997.
On a recent Saturday morning, Brabin is campaigning in the town of Batley. As she walks along the street, she greets everyone she passes with a cheery, "Hello, sweetheart, nice to see you!"
This is Brabin's home, and her love for the place -- and its people, her people -- is clear; representing them, she says, is "a real privilege."
It's Vintage Day, a highlight of the town's social calendar: A stage and stalls fill the Market Square, and classic cars are lined up in the streets nearby. People in period costumes dance to the swing music filling the air, while others shop for old-fashioned crockery and clothes.
Brabin, in a 50s-style rose-colored dress and feathered hat, has just come from the refreshments tent, where she spent time pouring cups of tea and selling cake to visitors.
As she hurries to her next appointment, she compliments others on their retro clothes: "Fab outfit!" -- and points out the local food bank, used by those struggling to afford grocery bills: "They handed out 8,000 meals last year, it's not right, is it?"
Brabin says a traumatic event while she was at university sparked her interest in social justice and politics: "I was attacked by a stranger in the street who tried to rape me," she explains. "It was horrible, I wouldn't wish it on anyone, but it was a defining moment; it made me a feminist."
Through her involvement in the women's movement, Brabin became more politically aware, campaigning against nuclear weapons and helping to support workers' families during the coal miners' strike of the mid-1980s.
A member of the Labour party for decades, she left temporarily in protest at the Iraq War.
Change of direction
It was Jo Cox
-- a long-time advocate for more women in parliament -- who suggested Brabin consider a move into politics.
"We were door-knocking in 2015 for her election, and I really enjoyed it," Brabin remembers. "I loved those conversations on the doorstep, and she said 'Tracy, you should think about a career in politics.'"
"It's something that I brushed to one side because there wasn't a vacancy for the place where I'd like to be the MP."
Brabin speaks warmly about Cox. "To see her in action, that was a masterclass in how to be an amazing MP -- she knew everyone, she had time and energy for everyone, she was full of love."
was "a complete waste," she says, adding that what happened means she has to stay fearless.
"Of all the MPs in Westminster, I must be the one who shows no fear, because if I hide away, they win. I have to live and get on with things. They can't win."
"What happened to Jo was a lightning bolt, but terror attacks in public places are something that could happen any time."
Indeed, when the Westminster attack happened a couple of months ago, Brabin found herself deluged with messages of concern and support from those she represents.
"It brought everything back (for them) -- that sense of panic and raised security," but it also highlighted to her how much support there was for her back home. "We care about each other."
Last month, Brabin's main opponent, Conservative Party candidate Ann Myatt, was forced to apologize
after telling voters "We've not yet shot anybody, so that's wonderful"
at a constituency meeting. Myatt, a consultant dermatologist, blamed tiredness for her "ill-judged" comments.
Taking over from her friend was, Brabin admits, a daunting task: "Coming in, I had to think -- obviously I'm not Jo -- so what can I bring to this? I have to make my mark in a different way."
Her strength, she decided, was her showbiz career and the skills and contacts it had equipped her with; she wants to use them to inspire local youngsters to take up careers in the creative arts.
She's helping to stage a youth production of Les Miserables
-- Cox's favorite musical -- in a disused mill in Batley
, and sees many more opportunities for culture to act as "an engine of regeneration" in what is, in parts, a deprived community.
In one of her first speeches to parliament, Brabin said Batley and Spen, once a powerhouse of manufacturing, had found itself left behind by globalization, with jobs for life replaced by less secure work.
It's this, Brabin believes, that led a majority here to vote "Leave" in the Brexit referendum. Like Cox, Brabin herself supported the remain campaign, but she voted to trigger Article 50 -- the mechanism for the UK to exit the union -- in line with the wishes of her voters.
"The people of Batley and Spen have spoken," she says. "But we didn't vote to lose jobs. We're leaving the EU, but we need to leave with the best deal.
After six months in parliament, Brabin was finding her feet, and so was somewhat unsettled to find herself back on the campaign trail again so soon. But she hopes to emerge after the June 8 vote with a clear mandate for the next five years.
This time around, "it's not a sympathy vote, it's not for Jo's sake, it's actually 'Who do we want in parliament? Who's got our back? Tracy.'"
Mostly, though, she's just desperate to get back to work.
"I feel this is the job of my life," she says. "I want to carry on -- there's so much to do!"