She is best known for her roles as Jean Weir on the NBC comedy-drama series Freaks and Geeks (1999–2000) and as Loreen Horvath on the HBO comedy-drama series Girls (2012–2017); Girls earned two Critics' Choice Television Award nominations and a Primetime Emmy Award nomination.

Baker's film credits include Jacob's Ladder (1990), In & Out (1997), A Simple Plan (1998), Stay (2005), Nights in Rodanthe (2008), Hope Springs (2012), Table 19 (2017), The Half of It (2020), and Holler (2020).

[2] Baker's film credits include Blue Steel, Jacob's Ladder, Lorenzo's Oil, Unstrung Heroes, Sabrina, Ridley Scott's White Squall, Men in Black, In & Out, Woody Allen's Celebrity, Sam Raimi's A Simple Plan (for which she received a Blockbuster Entertainment Award nomination), Two Weeks Notice, Steven Spielberg's War of the Worlds, Stay, The Night Listener, Death of a President, and Spider-Man 3.

She got her role in Freaks and Geeks after series creator Paul Feig and Judd Apatow saw her performance in Sam Raimi's A Simple Plan.

An accomplished stage performer, Baker made her Broadway debut in the 1981 production of The Best Little Whorehouse in Texas, and received a Drama-Logue Award in 1994 for her work in Night and Her Stars.