She represented the United States national team on 160 occasions, winning two FIFA Women's World Cups and an Olympic gold medal.

On September 21, 2024, she was put on the season-ending injury list due to chronic knee degeneration, thus effectively ending her career.

[11][12] She played on the Concorde Fire South '88 Elite that went on to win the 2007 GA U19G State Cup and advance to the Semi Finals of Regionals.

[13] A two-time Parade All-American coming into her freshman year at Stanford University, O'Hara led the Cardinal in scoring in 2006 with nine goals.

During O'Hara's junior year, Stanford advanced to the College Cup for the first time since 1993, defeating 2005 national champion Portland, 1–0.

[19] Prior to graduating from Stanford, O'Hara played for the Pali Blues of the USL W-League (semi-pro) in the summer of 2009, scoring four goals during her tenure with the club.

In addition to the close proximity of home stadium Pioneer Stadium to O'Hara's alma mater Stanford University, O'Hara had previously worked with FC Gold Pride head coach Albertin Montoya when he served as an assistant coach at Stanford University in 2008.

[22] As the regular season champion, the team earned a direct route to the championship playoff game where they faced the Philadelphia Independence.

[25] Despite their successful season, the club ceased operations on November 16, 2010, due to not meeting the league's financial reserve requirement.

[26] Because the club's head coach, Jim Gabarra, played O'Hara as a forward, she reverted to a role she filled with success in college.

[27][28] Over her career at Sky Blue, O'Hara has been played in several roles including forward, winger, right-back, and central midfielder.

[30] O'Hara contributed to Utah's first-ever franchise win, scoring a goal in the team's 2–0 victory over the Washington Spirit in May 2018.

She was still recuperating from an off-season ankle injury at the start of the NWSL season and saw limited minutes as a substitute in two late-April games.

Following her World Cup win, O'Hara started in two games for Utah at the end of July, notching an assist in the team's 2–2 draw against Portland.

[38] The Spirit won their first NWSL Championship on November 20, 2021, when they defeated the Chicago Red Stars, 2–1 in extra time at Lynn Family Stadium in Louisville, Kentucky.

[39] After the 2022 season, O'Hara announced on November 15 that she would sign with NJ/NY Gotham FC, returning to the club she formerly played for when it was called Sky Blue.

[43] On September 21, 2024, O'Hara was put on the season-ending injury list due to chronic knee degeneration, thus effectively ending her career.

O'Hara earned her first senior national team cap in March 2010, coming in as a substitute during a friendly match against Mexico.

After falling short of making the 21 player World Cup roster, O'Hara was called up to replace Lindsay Tarpley who tore her ACL in a send-off match against Japan on May 14, 2011.

[48] O'Hara earned just one cap at right midfield in the 2011 FIFA Women's World Cup in the final group stage game against Sweden.

[16] O'Hara started at right back against Costa Rica in the match that qualified the United States for the 2012 Summer Olympics in London.

[56][57] O'Hara made her second assist of the tournament in the semifinal against England when she delivered a cross from the right flank to Christen Press whose 10th minute goal put the U.S. in the lead.

[58] O'Hara started in the final against the Netherlands but was substituted at halftime due to a collision just before the break with the Dutch winger Lieke Martens.

[74][75] On April 23, 2024, O'Hara announced that she was one of the executive producers of "Ripe!," a queer short film in which two young women develop feelings for each other after a competitive moment in a pickup soccer game.

"Ripe!," which celebrates the ripening of LGBTQIA+ identities and shedding queer shame, premiered at the 2024 Tribeca Film Festival on June 9, 2024.