Létourneau made her MMA debut March 31, 2007 with TKO win over Tannaya Hantelman. Létourneau then lost her next two fights to future UFC Women's Bantamweights Sarah Kaufman & Alexis Davis. Létourneau broke her hand in the first round of her fight with Davis. After Létourneau rebounded by winning her next three fights she then set to face future UFC Women's Strawweight Cláudia Gadelha at Wreck MMA: Road to Glory. She lost via split decision. Létourneau returned at AFC 21 finishing off Jordan Moore in 34 seconds via TKO.
Létourneau made her UFC debut at UFC 174 taking on Elizabeth Phillips, who was filling in for the injured Milana Dudieva. Létourneau won the fight via split decision. Létourneau returned to the octagon to face fellow Canadian Jessica Rakoczy at UFC 186. Létourneau won the bout via unanimous decision. Létourneau next faced undefeated Maryna Moroz at UFC Fight Night 74. She won via unanimous decision. Létourneau faced Strawweight champion Joanna Jędrzejczyk on November 15, 2015 in the co-main event at UFC 193. She lost the fight by unanimous decision. Létourneau faced Joanne Calderwood at in the first ever women's flyweight bout in UFC history. She lost the fight via TKO in the third round. Létourneau faced Viviane Pereira at UFC 206. She lost the fight by a very controversial split decision and was subsequently released from the promotion.
Bellator MMA
On April 24, 2017, Létourneau signed a new contract with Bellator MMA. The deal enabled her to fight at a weight of 125 pounds, an easier weight cut than the 115 pound weight limit required for the UFC's strawweight division. Létourneau was expected to debut against Emily Ducote at Bellator 181 on July 14, 2017. However, on July 10, she pulled out of the bout due to injury. Létourneau eventually made her debut against Kate Jackson at Bellator 191 on December 15, 2017. She won the fight by unanimous decision. Letourneau then faced Kristina Williams at Bellator 201, earning the a unanimous decision victory. Letourneau faced Ilima-Lei Macfarlane at Bellator 213 for the Bellator Women's Flyweight World Championship. She was defeated by third round submission.
