Nelligan was born in London, Ontario, Canada, where she was raised by a factory father and a schoolteacher mother. Nelligan's childhood home life was a difficult one, with her mother struggling with alcoholism and crippling mental illness. Meanwhile, when she was a toddler, Nelligan was unable to walk due to illness. Figuring out her path as a youth also proved difficult, but at York University in Ontario she was steered towards acting by an insistent professor and decided to study drama in England. She tried to land a grant from the Canadian government to attend the prestigious Central School of Speech and Drama in London, but was denied federal assistance. Strapped for cash, Nelligan was financially endowed by a small number of Stratford board members in London. She finally moved to England and worked hard to ingrain the English dialect into her speech.The official start to Nelligan's professional acting career came with a 1972 production of Neil Simon's "Barefoot in the Park" at the Little Theatre in Bristol. She then moved on to the Old Vic for several plays, including productions of "Playboy of the Western World" and "A Streetcar Named Desire" between 1972 and 1973. In late 1973, she made the jump to television, delivering strong performances on episodes of "The Onedin Line" (1971-1980). In 1974, she received the Most Promising Actress award by the London Theatre Critics for her stage debut as Jenny in David Hare's "Knuckle." Her subsequent work opposite stage veteran Anthony Hopkins in the screen adaptation of David Mercer's play "The Arcata Promise" (1974) served to increase her in-demand performer status. In 1975, she played love interest Mercedes in the television version of "The Count of Monte Cristo" (NBC, 1975). Also that year, Nelligan made her feature film debut in "The Romantic Englishwoman" (1975). Nelligan continued to immerse herself in lofty roles of varying moral complexity. A turn as Rosalind in "As You Like It" at the Royal Shakespeare Theatre in 1977 was followed a year later by her much-lauded debut in the role of former WWII resistance member Susan Traherne of David Hare's "Plenty," a role that netted her Best Actress at the Olivier Awards. Proving her ability to roll with iconic material, she appeared in a 1979 production of The Bard's "Measure for Measure" on PBS. Later that year, she beguiled the infamous vampire (Frank Langella) in a feature remake of "Dracula" (1979). Throughout the 1980s, Nelligan continued along the same busy path she had established. She returned for a smoldering miniseries adaptation of "Thérèse Raquin" (PBS, 1981), playing the sexually frustrated title character, then had another juicy role as the lover of a German spy (Donald Sutherland) in "Eye of the Needle" (1981). Hot on the heels of the film's release, Nelligan moved to Los Angeles, but soon found herself struggling to find work and headed east for New York instead.Broadway stardom was in Nelligan's sights by 1982. Performing at the New York Shakespeare Festival, she reprised her role as Susan Traherne in "Plenty" before the play moved to an equally impressive run at the Plymouth in 1983. At the start of that year, she was appearing on movie screens once more as the harried mother of a disappeared child in "Without a Trace" (1983), before receiving a Tony Award nomination for "Plenty." A year later, Nelligan took on the part of Josie Hogan in "A Moon for the Misbegotten," which began at the American Repertory Theater in Cambridge before moving to the Cort on Broadway. She won her second Tony nomination. Nelligan returned to the big screen adaptation of Nicholas Gage's novel "Eleni" (1985). Playing opposite John Malkovich as titular character - the Greek mother of the journalist/author - the movie became a victim of misplaced accents, and wound up a critical and financial disaster upon release. Nelligan's plan to return to Los Angeles to retry her hand at a movie career had capsized, prompting her to continue performing on stage in New York instead. She was seen back at the New York Shakespeare Festival in the title role of "Virginia Woolf." In 1988, she defied critics of "Eleni" who wrote her off by appearing in a triumphant run of "Spoils of War," which bounced around Broadway stages in 1988 and landed her a third Tony nomination. That same year, she had a plethora of characters in "Serious Money," and at the 1989 Tony Awards, she found herself nominated a fourth time. Nelligan eventually proved to be a viable Hollywood asset after all, landing the plumb role of Lila Wingo Newbury, the relentless, prodding mother of Nick Nolte in "The Prince of Tides" (1991). She next had a small role in Woody Allen's murder mystery "Shadows & Fog" (1991), then was tapped by Garry Marshall for the role of Cora in "Frankie & Johnny" (1991). As 1991 came to a close, Nelligan's Hollywood fortunes continued to flourish. The National Board of Review named her Best Supporting Actress for "Prince of Tides." Then in 1992, she scored an Academy Award nomination for Best Supporting Actress for "Frankie and Johnny." After returning to work following the birth of her son, Gabriel, she had another award-worthy turn, this time on her home country's turf, with the Canadian series "Road to Avonlea" (CBC, 1989-1996), for which she nabbed an Emmy Award nomination for her role as Sidney Carver in 1992. Back on her home turf in Canada, she won a Gemini Award in 1993 for "Avonlea."Nelligan continued to alternate between television and film projects. She tried her hand at spoof comedy with Carl Reiner's "Fatal Beauty" (1993), then appeared in the television adaptation of "Spoils of War" (ABC, 1994). She squeezed in work on Mike Nichols' hairy male fantasy "Wolf" (1994) starring Jack Nicholson. Then over the next decade, Nelligan became a semi-regular presence in network movies of the week, mainly for CBS and ABC such as "Million Dollar Babies" (1994) and "Captive Heart: The James Mink Story" (1996). Her feature film resume also kept expanding with a vital presence in the intimate big screen dramas "Up Close and Personal" (1995) and "How to Make an American Quilt" (1996). Nelligan returned to the Broadway stage in 1997 as the senator's daughter in Wendy Wasserstein's "An American Daughter" at the Cort. Then in 1998, she put a little action into the movie mix playing U.S. Marshal Walsh in the big-budget action flick "U.S. Marshalls" (1998). By late 1998, Nelligan was off to New England to film a part in the adaptation of John Irving's acclaimed novel, "The Cider House Rules" (1999). Along with her castmates, she shared in a nomination for Best Ensemble Cast at the Screen Actors Guild Awards in 2000. She immediately dove into a string of telefilms, starting with the legal drama "Swing Vote" (ABC, 1999). She segued into "William and Henry" (Showtime, 2001) playing the calm-headed Aunt Elizabeth, then returned to ABC for the role of interplanetary guide Mrs. Which in its much-anticipated "A Wrinkle in Time." With the freedom to pick and choose her roles, Nelligan worked less frequently into the 2000s. She did make time to take on a personal project - editing and producing a documentary entitled "The Breast Cancer Diaries" (2006). Shortly before its festival debut in 2006, she went back for another helping of onscreen parenting as the concerned mother to Sandra Bullock in the feature thriller "Premonition" (2007).