Frum was born in Toronto, Ontario, the daughter of Barbara Frum, a journalist, and Murray Frum, a real estate developer. Her brother David Frum is a political author and journalist, and was a speech writer for George W. Bush and helped coin the phrase "Axis of Evil". Another brother, Matthew Frum, was adopted and is of aboriginal ancestry. Frum attended Havergal College and received a Bachelor of Arts degree from McGill University, Montreal in 1984. In June 2010, she received an Honorary Doctorate from Yeshiva University.
She has authored two books, Linda Frum's Guide to Canadian Universities (1987, with an updated edition published in 1990) and Barbara Frum: A Daughter's Memoir (1996). Frum is a former contributing editor to Maclean's, and was a columnist with the National Post from 1998 to 2002 and again from 2006 to 2007. In 1996 she won a Gemini Award for Best Social-Political Documentary Program for the film Ms. Conceptions.
She has served as a volunteer for many community organizations. She is a member of the Board of Mount Sinai Hospital in Toronto. She and husband Howard Sokolowski recently endowed The Sokolowski/Frum Reception, Triage and Waiting Area with a $5 million gift to the Hospital. She is a former vice-chair of the board of governors of Upper Canada College and a former member of the board of the Bishop Strachan School in Toronto. She is honorary patron of the Leukemia and Lymphoma Society of Canada. In 2006, she was chair of the Women's Division of the United Jewish Appeal. She is a past board member of the Canada Israel Committee, the Art Gallery of Ontario Foundation, Soulpepper Theatre, and the Ontario Arts Council.
Frum lives in Toronto with her husband Howard Sokolowski, a real estate developer and former co-owner of the Toronto Argonauts of the Canadian Football League, and her three children. In 2006, she and her husband received the Human Relations Award from the Canadian Council of Christians and Jews.
On August 27, 2009, she was appointed to the Senate by Prime Minister Stephen Harper. She has a Conservative affiliation and represents Ontario. She was elected Chair of the Conservative Senate Caucus in October 2015. She currently serves on the Social Affairs, Science and Technology committee, the Rules committee, the Human Rights committee and the Senate's Conflict of Interest Committee.
In 2012, Minister Jason Kenney appointed Senator Frum Co-Chair of the Advisory Council for the 2013 Task Force for International Cooperation on Holocaust Education, Remembrance, and Research. In 2013, Minister Ambrose appointed Frum to sit on a task force to promote the participation of women on corporate boards. In December 2013, Frum and her husband co-chaired the Jewish National Fund's Negev Dinner in honour of Prime Minister Harper. The dinner set records for both attendance and fundraising: 4,000 people attended and $5.7m was raised for the Stephen J. Harper Bird Sanctuary Visitor and Education Centre in Hula Valley, Israel.
Frum ran for the position of Conservative caucus leader in the Senate, which would have also made her Senate Opposition Leader, but was defeated on March 28, 2017, by Senator Larry Smith.