Grégoire was born on April 24, 1975, in Montreal, Quebec, the only child of Jean Grégoire, a stockbroker, and Estelle Blais, a Franco-Ontarian nurse. Her family lived north of the city, in Sainte-Adèle, eventually relocating to Montreal when she was four years old. She was raised thereafter in Montreal’s Mount Royal suburb, where she was a classmate and childhood friend of Michel Trudeau, the youngest son of Prime Minister Pierre Trudeau and his wife Margaret; and brother of Grégoire’s future husband, Justin Trudeau.

Grégoire first met Justin Trudeau, the eldest son of Prime Minister Pierre Trudeau, when they were both children in Montreal, where Grégoire was a classmate and childhood friend of the youngest Trudeau son, Michel. Grégoire and Trudeau reconnected as adults in June 2003, when they were assigned to co-host a charity ball, and began dating several months later. They became engaged in October 2004, and married on May 28, 2005, in a ceremony at Montreal’s Sainte-Madeleine d’Outremont Church. They have three children: Xavier James born in 2007, Ella-Grace Margaret born in 2009, and Hadrien Gregoire born in 2014.

In 2005, Grégoire attended a charity function where she met several CTV Television Network employees. This led to her being hired in September 2005 as a reporter for eTalk, CTV’s Canadian entertainment news show. She served until 2010 as eTalk’s Quebec correspondent, and focused her reporting on the philanthropy and activism of celebrities.

As part of her work with WaterCan, Grégoire travelled to Ethiopia in October 2006 with her mother-in-law, Margaret Trudeau, who is the honorary president of the organization. Their trip was featured in a CTV documentary, “A Window Opens: Margaret and Sophie in Ethiopia”, which aired in May 2007.

After her husband became a Member of Parliament for Montreal’s Papineau riding in 2008, Grégoire continued to live in their Montreal home with their children, while Trudeau stayed at a hotel in Ottawa during the week. In June 2013, two months after Trudeau became the leader of the Liberal Party of Canada, the couple sold their home in Montreal’s Côte-des-Neiges neighbourhood and began living in a rented home in the Rockcliffe Park area of Ottawa.

Grégoire is fluent in French, English, and Spanish. She became a certified yoga instructor in 2012.

Grégoire Trudeau’s husband Justin Trudeau was officially sworn in as the Prime Minister of Canada on November 4, 2015. After the end of the 2015 election, Grégoire Trudeau indicated her preference for the hyphenated surname of “Grégoire-Trudeau”, but she switched to using the unhyphenated form in March 2016.

On January 18, 2016, Grégoire Trudeau made the impromptu decision to sing a work she composed, entitled “Smile Back at Me” at the end of a speech in honour of Martin Luther King, Jr. Day at Ottawa City Hall. Mike Strobel, of the Toronto Sun, said the crowd gave her a standing ovation. Toronto Star pop music critic Ben Rayner said the song was “out of pitch” and “cast serious doubt upon her musical judgment”. In Maclean’s, Michael Barclay (formerly a music critic), described the song as “fine”, although not designed to be sung a capella, and that Grégoire’s voice was “surprisingly strong”. Remixed versions of the song were released online afterward.

On March 12, 2020, Grégoire isolated herself at Rideau Cottage, along with her husband and children, after she showed flu-like symptoms during the COVID-19 pandemic, shortly after she returned from a speaking engagement in the United Kingdom. The Prime Minister’s Office announced later that day that she had tested positive for COVID-19. By March 28, she had recovered.