Born in Thornton, Colorado to Mike and Kelly Marshall, Nikki was raised with her younger sister, Shaye, in Mead, Colorado. She attended Skyline High School in the nearby city of Longmont and was the leading scorer for the soccer team. She was named All-State three times during her sophomore, junior and senior years and was a three-time Longmont Times-Call Soccer Player of the Year. Marshall finished her high school career with 100 goals and 38 assists. She graduated as the top scorer in the school's history. She scored 23 goals and served 10 assists during her senior year alone and was named 2006 Northern Conference Player of the Year, all-region soccer player of the year, and Skyline Falcon of the Year. Also a decorated track athlete at the school, she earned All-State honors in the 100 meter, 400 meter relay and long jump during her junior year and won the state championship in the 800 medley as a senior.
Colorado Buffaloes
Marshall currently holds seventeen school records for the University of Colorado, and is the all-time leading goal scorer for the Colorado women's soccer team. As a freshman, she led the Buffaloes' most prolific offensive season with seventeen goals, all the way to the Sweet Sixteen in the 2006 NCAA postseason. She was on Soccer Buzz's All-American Fourth Team, All-American Freshman Team, All-Central Region First Team, All-Central Region Freshman team, and Freshman of the Year. She was on the Freshman All-American Team in Soccer America and National Player of the Week in Soccer Times. Her Big 12 Conference awards in 2006 include Newcomer of the Year, First Team All-Big 12, All-Big 12 Newcomer Team, and Big 12 All-Tournament Team. The University of Colorado Athletic Department awarded her Female Athlete of the Year and Female Freshman of the Year. In 2007, Marshall led the Buffaloes in scoring for the second-straight year with nine goals, even though she had played defender that year for Colorado. Before her sophomore year season, she Marshall was on the Pre-season All-American Team by Soccer America and was ranked Pre-season All-Big 12 by the Big 12 Conference. She was runner-up in the most playing time on the team, totaling 1,927 minutes on the season. She led the Buffs to 10-8-4 record and another bid into the NCAA tournament She ended the season with a First Team All-Big 12 award from the Big 12 Conference. During her junior year, Marshall was moved back up to the striker position. She was ranked Pre-season All-Big 12 by the Big 12 Conference. After another successful season, Marshall was second on the team for goals scored, with eight goals. She led her team second in the Big 12 Tournament and a bid to the NCAA Tournament. For the third year in a row, she received First Team All-Big 12 from the Big 12 Conference. In 2009, Marshall was again ranked a Pre-season All-American by Soccer America. She was captain of the Buffaloes along with fellow senior Kara Linder. She led the Buffs in scoring with a total of eight goals on the season. She also let the team in number of shots taken, 53. She finished the season with another First Team All-Big 12 accolade.
Playing career
Club
The WPS Years, 2010–11
Marshall was the first draft pick for the Washington Freedom in the 2010 WPS Draft. During the 2010 season, she started in all 24 of the team's regular season matches and scored three goals playing as a defender. The Freedom finished fourth during the regular season with an 8–7–9 record, earning a berth to the playoffs. During the playoff quarterfinals, the Freedom were defeated by the Philadelphia Independence 1–0. Marshall remained with the club in 2011 when they relocated to Florida and became magicJack under new ownership. She played in eight games for magicJack before being traded to the Boston Breakers. She made seven appearances for the Breakers as the team finished fourth in the regular season with a 5–4–0 record. On August 17, 2011, the Breakers were defeated 3–1 by magicJack and eliminated from the playoffs.
In February 2013, Marshall signed with Portland Thorns FC for the inaugural season of the National Women's Soccer League. She was on the starting lineup as a defender in all of the Thorns' 22 games as the team finished third in regular season play and received a berth to the playoffs. During the team's playoff semi-final match, Marshall served the assist to Tiffany Weimer's equalizer goal. The Thorns would eventually defeat FC Kansas City 3-2 in overtime. The Thorns defeated Western New York Flash during the playoff final clinching the league's first championship title. Marshall was waived by the Thorns during the post-season and picked up during the waiver draft by the Washington Spirit. A few months later, she was traded to the Seattle Reign FC. In December 2013, she was traded back to the Portland Thorns. Thorns management clarified that Marshall was put on waivers due to a cap issue. With the trades, she was signed to a new contract at a different salary for the 2014 season. During the 2014 season, Marshall started in all 24 matches for the Thorns playing for 2072 minutes. After finishing third during the regular season with a record, the Thorns advanced to the playoffs where they were defeated in the semifinals 2-0 by eventual champions FC Kansas City. In August 2014, Marshall suffered an anterior cruciate ligament tear during a match against the Seattle Reign. She announced her retirement in February 2015, citing low pay.
