She previously played for Chicago Red Stars, Boston Breakers, and magicJack in Women's Professional Soccer as well as the Portland Thorns FC and Houston Dash in the NWSL.

[6] In preparation for her senior year at North Carolina, Washington played for Pali Blues, scoring six goals and providing two assists.

Blues head coach Charlie Naimo said of her, "Nikki brings a lot of experience at a young age.

[16] The club won the Western Conference championship after defeating the Sounders Women 1–0 on July 22 in Fullerton, California.

[20] In February 2013, it was announced that Washington had signed with the Portland Thorns for the inaugural season of the National Women's Soccer League.

[22] After finishing third during the regular season and advancing to the playoffs, Portland captured the inaugural National Women's Soccer League championship title on August 21 after defeating regular season champions Western New York Flash 2–0 in Rochester, New York.

[23] In January 2014, Washington was traded to expansion team Houston Dash during the 2014 NWSL College Draft.

Dash head coach Randy Waldrum said, "With the trade, we were able to acquire Nikki Washington, a Texas native, who has played in both the WPS and NWSL.

"[13] Washington captained the United States team that won the 2008 FIFA U-20 Women's World Cup and played 65 minutes during the final against North Korea.

[26] In the summer of 2015, she joined Texas Christian University women's soccer team as the Director of Operations.