A four-year varsity girl’s soccer player at Mount Notre Dame High School, Lavelle was named Cincinnati’s Player of the Year by The Cincinnati Enquirer her senior year. The same year, she scored 15 goals (38 points) for her team. Lavelle finished her high school career as the team’s leading scorer with 57 goals. She was twice-named NSCAA All-Region as a junior and senior and received first-team all-state honors. She was awarded the Greater Cincinnati/Northern Kentucky Sports Women of the Year award in 2013.

Lavelle was accepted to play college soccer at the University of Wisconsin–Madison in 2013. A four-year starter, Lavelle made 19 appearances as a freshman, scoring 6 goals and registering 7 assists on the way to being named Big Ten Conference Freshman of the Year. Wisconsin won the Big Ten Women’s Soccer Tournament in 2014. Lavelle was named Big Ten midfielder of the year consecutively in 2015 and 2016. In 2015, she was also named first-team All-American by the National Soccer Coaches Association of America (NSCAA), the first Wisconsin Badger to do so since 1991.

Lavelle represented the United States at multiple youth levels. On November 24, 2015, Lavelle was called up to train with the senior United States women’s national soccer team. One of eight players who joined the team’s Victory Tour following the 2015 Women’s World Cup, she earned her first senior international cap on March 4, 2017, during a match against England at the 2017 SheBelieves Cup. She was named Player of the Match following the team’s 1–0 loss.

On January 12, 2017, Lavelle was selected number one overall at the 2017 NWSL College Draft by the Boston Breakers. Lavelle started her professional career by scoring two goals in eight games and was named Player of the Month for April. However, after suffering a hamstring injury in June while on international duty, Lavelle missed over two months and finished the season with only ten appearances as a rookie. The Breakers folded before the start of the 2018 season.

A dispersal draft was held by the NWSL to distribute Breakers players across the league. Lavelle was selected first overall by Washington Spirit, who acquired the first pick through a trade with Sky Blue FC. Due to injury and international duty Lavelle only appeared in eleven games for the Spirit in 2018. Despite only making six appearances the following year due to international duty, scoring one goal and recording one assist, Lavelle was named to the 2019 NWSL Best XI in the end of the season awards. With the 2020 season affected by the COVID-19 pandemic, Lavelle took part in the 2020 NWSL Challenge Cup, making four appearances and scoring one goal as Washington finished second in the preliminary group but were eliminated in the first knockout round by Sky Blue FC on penalties.

In September 2018, Lavelle was named to the national team roster for the 2018 CONCACAF Women’s Championship, the qualifying tournament for the 2019 FIFA Women’s World Cup. She appeared in all five games for the U.S. and scored three goals. Her final goal of the tournament was scored in the second minute of the championship game against Canada, helping the U.S to a 2–0 victory, and their second straight CONCACAF Championship.

Lavelle was named one of the world’s top 11 players by The Best FIFA Football Awards 2019 (finishing sixth), and was chosen as one of the world’s top three midfielders by her professional peers in the 2019 FIFA FIFPro World XI.

On August 16, 2020, Lavelle was traded to OL Reign in exchange for OL Reign’s natural first-round pick in the 2022 NWSL College Draft, $100,000 in allocation money and further performance-based allocation money with the acknowledgement that she would be signing outside the league.

On August 18, 2020, Lavelle signed with Manchester City of the English FA WSL ahead of the 2020–21 season.

In 2020, Lavelle was named a brand ambassador for FLIGHT by Yuengling, a premium light beer.