McIntosh was two when her family moved to Toronto. She was educated at Vaughan Road Academy, the University of Toronto and the American Repertory Theatre Institute at Harvard University. She studied English and drama at university, becoming a teacher for several years.

She made her Stratford Festival debut in 1992, appearing in Two Gentlemen of Verona. Other roles at that time included Iras, one of Cleopatra's servants, in Antony and Cleopatra (1993) and Maria in Twelfth Night (1994).

Back in Toronto, McIntosh played Helena in the Canadian Stage Company's A Midsummer Night's Dream (1996), winning a Dora Award nomination. Her first Dora came in 1998 when she starred in Athol Fugard's Valley Song, directed by Seana McKenna. A remarkable performance in the title role of Florence Gibson's Belle (Factory Theatre, 2002) brought another Dora nomination.

Never one to back away from a challenge, Yanna McIntosh made a fierce, dominating Petruchio in a gender-bending Taming of the Shrew (Canadian Stage, 2000). Skylight, directed by Dennis Garnhum at Tarragon Theatre in 2001, earned her a second Dora Award. McIntosh alternated with Caroline Cave in a critically acclaimed production of Pamela Gien's demanding one-person show The Syringa Tree (Canadian Stage, 2004). Both were nominated for Doras; Cave won.

Yet more Dora nominations followed for Hedda Gabbler, directed by Volcano Theatre's Ross Manson at Buddies in Bad Times Theatre in 2005, and for The Monument, directed by Nigel Shawn Williams for Obsidian Theatre in 2006.

Among other noteworthy performances in Toronto were Mary Stuart in Schiller's play of the same name (Soulpepper, 2007); the role of Condoleezza Rice in the Studio 180 production of Stuff Happens in 2008; and Maud/Victoria in Cloud Nine for Mirvish Productions in 2010. The following year, McIntosh received both a Dora Award and an inaugural Toronto Theatre Critics Award for her incandescent performance as Mama Nadi in Lynn Nottage's Ruined, produced by Obsidian and Nightwood Theatre.

McIntosh returned to the Stratford Festival in 2008, this time in starring roles. Highlights include playing Helen in The Trojan Women, directed by Marti Maraden in 2008; Lady Macbeth in a production directed by Des McAnuff and Titania in A Midsummer Night's Dream (both 2009); Madame Volanges in Dangerous Liaisons and Hermione in The Winter's Tale (both 2010); and Queen Elizabeth in Richard III (2011).

Yanna McIntosh has had recurring roles in several TV series, including that of Jenni Hernandez in the CBC soap opera Riverdale (1997–99), Edna Myles in The Eleventh Hour (CTV, 2002) and Zona Robinson in CBC's This is Wonderland. Other TV credits include Doomstown (2006, for which she won a Gemini Award), Finn's Girl (2007), The Sentinel (2006) and A Raisin in the Sun (2008). She also appeared in Deepa Mehta's film Heaven on Earth (2008).

Yanna McIntosh has taught at the National Theatre School in Montréal and at Humber College in Toronto.