Ertz played collegiate soccer with the Santa Clara University Broncos from 2010 to 2013. Following her collegiate career, Ertz was selected third overall by the Chicago Red Stars in the 2014 NWSL College Draft that took place on January 17, 2014. Ertz helped the United States win their titles at the 2015 and 2019 FIFA Women's World Cup. At 23, she was the second youngest member of the 2015 team behind 22-year-old Morgan Brian. The United States went on to the World Cup final where she played every minute of all seven games of the tournament and was subsequently named to the FIFA Women's World Cup All-Star Team.