Landsberg grew up in Toronto, acquiring values and grammar from her strict immigrant mother. After graduating with a bachelors degree in English from the University of Toronto in 1962, she worked for The Globe and Mail, raised her family, freelanced, and joined Chatelaine as a staff writer/editor. She joined the Toronto Star as a columnist in 1978, then wrote a weekly column for the Globe and Mail in the 1980s.

Landsberg has written three best-selling books: Women and Children First, a collection of her campaigning columns, Michele Landsberg's Guide to Children's Books, and "This is New York, Honey!" A Homage to Manhattan, with Love and Rage, a memoir of her time living as the spouse of Canada's ambassador to the United Nations. Other distinctions include two National Newspaper Awards, the YWCA Women of Distinction Award, the Dodi Robb award from MediaWatch, the Robertine Barry Prize, the Florence Bird Award from the International Centre for Human Rights, the Canadian Governor General's Award in Commemoration of the Persons Case and Democratic Development. She has also received several honorary degrees from such institutions as McMaster University.

Landsberg's writing tends to be both analytical and realistic, often including descriptions of physical experiences, from nursing an infant to dieting or quitting smoking. Some feel she detracted from the power of her message by resorting too frequently to name calling and stereotyping, e.g. she unfailingly referred to Conservative politicians with epithets such as "jack-booted Tories" and "Harris's henchmen". Her feminism includes strong expressions about the need to provide time and resources for maternal leave, and also excellent childcare programs. She also often devotes herself to in-depth analysis of facts that she feels have received an anti-woman spin by other media. A piece debunking coverage of a divorce decision, for example, can be found online.

In 2000, she especially angered transsexual activists with a column in the Toronto Star entitled "Rape crisis centre in B.C. endures assault", in which Landsberg remarks that "If a man cuts off his penis, pumps himself full of hormones, gets silicone breasts and electrolysis, and stuffs his feet into high heels is he/she a woman?" She also said part of her would always be "outraged.."that 'woman' could be defined as an outward set of physical characteristics - lack of penis, fake breasts - along with an ultra-sexist 'female impersonator' style of clothing and gesture."

Landsberg is married to UN Special Envoy Stephen Lewis. Their children are Ilana Naomi Landsberg-Lewis, Jenny Leah Lewis and journalist Avi Lewis, who is married to writer Naomi Klein.

In 2005, the Canadian Women's Foundation named a new award after Landsberg, to honour young women 18 to 30 who are outstanding in media and activism.

In 2006, she was made an Officer of the Order of Canada.