Meigs was born in Philadelphia and raised in Washington, DC. She studied at Bryn Mawr College, and subsequently taught English literature and creative writing at that school. She served in the United States Navy's WAVES corps during World War II.
She subsequently studied art in New York City, and had her first exhibition of paintings in 1950.
Openly lesbian, Meigs met author Barbara Deming in 1954. Deming and Meigs became a couple and moved to Wellfleet, Massachusetts, where they joined a Cape Cod artistic circle that included abstract painter Mark Rothko, critic Edmund Wilson, and writer Mary McCarthy.
In 1963, Wilson introduced Meigs to Marie-Claire Blais, a writer from Quebec who became romantically involved with Meigs and Deming, and moved to Brittany with Meigs in 1972. The couple subsequently returned to Montreal, where Meigs spent the remainder of her life, in 1976.
Also in the 1970s, Meigs returned to writing, publishing books such as Lily Briscoe: A Self-Portrait (1981), The Medusa Head (1983) and The Box Closet (1987). In addition to her writing, she became a prominent spokesperson in Canada for lesbian, feminist and seniors' issues. She died in Montreal in 2002, following a series of strokes.