Barnhart was one of the original members of the NWSL, being allocated to FC Kansas City in 2013. She played 108 matches for FCKC, which included two championships before the team was moved to Utah to become the Utah Royals. Barnhart played 32 matches for the Royals before returning to Kansas City in 2021 when the roster from the Royals was transferred to the Kansas City Current. Prior to the NWSL, Barnhart played for the California Storm of the WPSL and FC Gold Pride and the Philadelphia Independence, both of the WPS. Barnhart has twice won Goalkeeper of the Year, the first coming in the WPS in 2010 and again in 2013 during the inaugural season of the NWSL.
On top of a successful club career, Barnhart was a mainstay on the USWNT as the backup to Hope Solo from 2004-2013. With the USWNT, she won Olympic gold twice.
At Stanford, Barnhart was a two-time first-team All-American. She shares the all-time record for shutouts at Stanford with Houston’s Jane Campbell at 35 and holds the single-season record for shutouts with 18. Barnhart also holds the single-season record for goals-against average at 0.19.