A native Texan from Rowlett Marissa Diggs lettered all four years of high school playing soccer and was the captain of the varsity team in 2009. She was named the Rowlett High School Defensive Player of the Year in 2009. She also played for Polaris '92 and Sting '92 as a youth. Competing in the North Texas State Cup finals, the Disney Showcase Predator Flight title and the Spring Classic title in 2007 with Polaris '92.
After high school Diggs began attending and playing for the University of Central Florida in Orlando, Florida. As a freshman she had 17 starts appearing in 23 matches for the Knights on the backline. She scored against Marshall and Southern Miss during the 2010 season. As a sophomore in 2011 she started all 24 matches including four matches in the NCAA Championship. She once again scored against Southern Miss as well as against San Diego State. At the end of the season she earned All-Conference USA First Team honors and was selected to the NSCAA All-Central Region First Team. Her junior year she was a part of the back line that helped the team record 15 shut outs on the season, a C-USA single season record. Diggs scored the game winning goal in the teams win against Florida Gulf Coast on August 19. The Knights won their first conference tournament title that year with Diggs being named the C-USA Tournament Defensive MVP as well as being named to the All-Tournament team. At the end of the season she was named a NSCAA Second Team All-American, the C-USA Defensive Player of the Year and a C-USA First Team selection. In her final season with UCF Diggs started all 23 games playing 2155 minutes. It was the only season defending for the Knights she didn't score a goal but she did have a game winning assist on Alex Piercy's goal against UConn. She was a Hermann Trophy Watch List candidate and American Preseason Defensive Player of the Year. With UCF now a part of the American Athletic Conference Diggs was the conference's Defender of the Week for 9/16 after shutout wins over Stetson and Brown. The Knights went undefeated in conference play that year and won the AAC regular season title. Diggs finished the year by being named the American Athletic Conference Defensive Player of the Year and All-Conference First Team. She was rated #1 in the American Athletic Conference by TopDrawerSoccer.com and tenth nationally.
Diggs was taken in the second round, 11th overall, by the Houston Dash in the 2014 NWSL College Draft. She is a very strong and physical defender. She also has the ability to play as a holding midfielder in addition to her usual position of center back. Versatility and physicality are two traits that head coach Randy Waldrum loves to have in his players and Marissa Diggs is exactly the type of player he will want on the back line.