She is a member of the New Democratic Party (NDP).
In Brosseau's first election campaign, she gained national attention for her surprising rise from a "paper candidate" to a viable contestant, and gained the nickname "Vegas Girl" for a mid-election vacation to Las Vegas.
She won reelection in the 2015 election with a larger vote share despite her party falling from second to third place nationally.
Her parliamentary roles included House Leader of the NDP, critic for Agriculture and Agri-Food, and deputy NDP caucus chair.