Long attended Northport High School from 2001 to 2005, where she played varsity soccer for four years. Long helped her high school team go undefeated in the regular season for all four years. In 2005, Northport advanced to the Long Island semifinals. Long was named to the All-State first team and All-County team all four years at Northport. After her junior and senior year, she was Newsday's Player of the Year and Suffolk County Player of the Year. Long also made the All-Long Island Team for her last two years at Northport.
Long attended Pennsylvania State University from 2005–2006. During her freshman year in 2005, she appeared in all 25 games, starting 22. After starting the first game, she entered the starting lineup permanently in the fifth game of the season, remaining there for the balance of the Lions' 23–0–2 season. She scored four goals on 58 shots and had six assists for the season. Long was a 2005 National Soccer Coaches Association of America Third-Team All-Mid-Atlantic Region selection and was named to the Soccer Buzz second-team All-Mid-Atlantic Region, Soccer Buzz second-team freshman All-America squad, and was tapped for the Soccer Buzz 2005 Freshman All-Mid-Atlantic Region Team. She was also named to the second-team All-Big Ten squad and the All-Tournament Team at the 2005 Big Ten Tournament and earned Big Ten All-Freshman Team honors.
Long represented the United States on the U-20 and U-23 national teams and was a member of the 2006 U-20 Women's World Championship team. She was called up to the full national team in July 2010.
During her junior year in 2007, Long transferred to the University of North Carolina at Chapel Hill. She appeared in all 24 games, starting in 22. Long scored five goals during the season. She picked up her first two goals as a Tar Heel against Yale for her only multiple goal game of the season, for which she was named to Soccer America, Soccer Buzz and Top Drawer Soccer National Teams of the Week. She was also on the watchlist for the Hermann Trophy.
On January 16, 2009, Long was selected seventh overall in the first round of the 2009 Women's Professional Soccer Draft by the Washington Freedom for the inaugural 2009 WPS season. She made her first appearance for the team on March 29, 2009 in a match against the Los Angeles Sol. During the 2009 regular season, Long made 18 appearances for the Freedom, helping the team finish third in the WPS. She also made two goals during the regular season. The Freedom faced Sky Blue FC in the first round of the playoffs on August 15 and were defeated 2–1, ending their advancement in the postseason tournament. Long remained with the Washington Freedom for the 2010 WPS season. Long scored the lone goal in the team's opening game of the season on April 10 against the Boston Breakers. She went on to make 21 appearances for the Freedom in the regular season and scored two goals. The Freedom finished fourth in the WPS after the regular season but were defeated by the Philadelphia Independence in the first round of the playoffs on September 19.
Immediately following the 2011 WPS season, Long played for Paris Saint-Germain in the Division 1 Féminine in France for the 2011–2012 season, which ran from September to June. She first made an appearance for the team on October 16, 2011 in a match against FF Yzeure Allier Auvergne. She made 12 appearances for the team, starting nine, and scored four goals. Her last appearance for the team was on March 25, 2012.
On January 30, 2012, it was announced that the 2012 WPS season would be suspended following legal and financial challenges. Although the league was intended to resume for the 2013 season, it officially folded in May. In April 2012, Long signed with the New York Fury in the Women's Premier Soccer League Elite, a semi-professional soccer league created by the WPSL in response to the suspension of the WPS. The Fury finished third in the league and qualified for the playoffs. The Fury faced the Western New York Flash on July 25, 2012 in the semifinals. Long scored the Fury's lone goal of the match and the team was defeated 2–1.
On January 17, 2013, it was revealed that Long had signed with the Portland Thorns FC of the newly formed National Women's Soccer League for the 2013 season. Following the American season, Long agreed to an off-season loan to Chelsea Ladies. She traveled to Japan for the English team's International Women's Club Championship campaign. Long became one of Portland's top players over the years, scoring the most goals in the 2015 season and leading the team to the title in 2013, the semifinal in 2014 and 2016, and the title again in 2017. At the end of the Thorns' 2017 season, she had the most appearances for the team over its five seasons and was its second-leading scorer, one goal behind captain Christine Sinclair.
On May 8, 2014 Long made her international debut for the United States senior women's team against Canada in a friendly match at Winnipeg; entering the match at the 68th minute. She scored her first and second goals in a friendly against Colombia on April 6, 2016, in East Hartford at Renschler Field.
In late October 2016, Long married longtime boyfriend Jose Batista.
On January 11, 2018, Long was traded to the Seattle Reign FC in exchange for Australian international forward Caitlin Foord and a 2020 NWSL 2nd Round draft pick.
