Canberra United FC, 2013 Mewis signed with the Australian
W-League team
Canberra United FC to finish the final two weeks of the
2012–13 season. She made her first appearance for the club during a 5–0 win against the
Western Sydney Wanderers FC on January 8 and scored the team's fifth goal in the 89th minute of the match. Her second and final appearance occurred on January 12 when the team was defeated 5–1 by eventual regular season champions,
Brisbane Roar FC. Mewis scored Canberra's only goal of the match in the 45th minute. Canberra United finished fifth during the regular season with a 5–3–4 record.
FC Kansas City, 2013 In January 2013, Mewis was drafted in the first round (third pick overall) of the
2013 NWSL College Draft to
FC Kansas City for the
inaugural season of the
National Women's Soccer League. She was elevated to U.S. Soccer-subsidized status during the year. She started in the league's inaugural match on April 13, 2013, as Kansas City drew 1–1 against the Portland Thorns, also the game in which she became the first player in NWSL history to be shown a yellow card. She scored her first goal of the season in the 74th minute of the Blues' 3–2 win over
Portland Thorns FC on May 8. Mewis made 20 starts as a rookie for FC Kansas City during the
regular season helping the team finish second in the standings with an 11–5–6 record. The team advanced to the playoffs but were defeated 3–2 in the semifinals by Portland.
Boston Breakers, 2014–2016 In November 2013, FC Kansas City traded Mewis to
Seattle Reign FC for
Amy Rodriguez. Of the trade, Reign FC coach,
Laura Harvey said, "Kristie is a young, bright and talented player who we feel can benefit our long-term plan. She has proven that she can be a high-level player in this environment and we feel we have the structure to help push Kristie to the next level." On November 18, 2013, she was traded alongside
Michelle Betos and two 2015 NWSL College Draft picks to the
Boston Breakers for
Sydney Leroux. She started in 15 games and scored 3 goals in 2014 for the Breakers.
Iga FC Kunoichi, 2014 (loan) October 2014 Mewis signed a three-month contract with
Iga FC Kunoichi of the Japanese
Nadeshiko League first division. Wearing number 31 and playing as a forward, Mewis scored five goals in seven games, which included two braces. During matches in which she played, Iga FC compiled a record of 6–1.
FC Bayern Munich, 2015 (loan) In August 2015, Mewis signed a one-year contract with
Bayern Munich.
Washington Spirit, 2016–2017 In November 2016, Mewis was traded along with
Kassey Kallman from the Boston Breakers to the
Washington Spirit for
Megan Oyster.
Chicago Red Stars, 2017 On August 21, 2017, Mewis was traded to the Chicago Red Stars for their first round draft pick in the 2018 NWSL College Draft. In her first and only game for the Red Stars (against her previous team), she scored a goal in the first half helping to secure a victory for the Red Stars and eliminating the Spirit from playoff contention.
Houston Dash, 2017–2021 On August 30, 2017, about a week after being traded to the Chicago Red Stars, Mewis was traded to the
Houston Dash for USWNT player
Morgan Brian with additional, undisclosed future considerations going to Houston. Mewis was voted onto the NWSL's May 2018 Team of the Month. During a game in May 2018 vs the Washington Spirit, Mewis tore her ACL. Mewis returned stronger in 2019 with a new mindset stating: "Me tearing my ACL was kind of a blessing in disguise because I feel like it just woke me up a little bit. It just made me ask myself, 'Kristie, what are you doing? You need to come back from this. You're being OK with being 70 or 80 percent,'" she continued, "It was just hard to admit to myself that I wasn't happy with where I was. But I think I just woke up one day and was like, 'Let's do this.'". The next year, Mewis would go on to help the Houston Dash win their first trophy at the
2020 NWSL Challenge Cup.
Gotham FC, 2022–2023 On December 16, 2021, Mewis was selected by NWSL expansion club
San Diego Wave FC in the
2022 NWSL Expansion Draft and subsequently traded to Gotham FC in exchange for $200,000 in
allocation money. In the
2023 NWSL semifinal, Mewis made an assist to
Katie Stengel, who made the game 1–0 against
Portland Thorns and sent Gotham FC to the final, where they won. In December 2023, Mewis and Gotham FC mutually agreed to part ways.
West Ham United, 2023–2025 On December 22, 2023, Mewis joined
Women's Super League club,
West Ham United. She made her debut for the club on January 21, 2024, coming on as a substitute for
Honoka Hayashi in the 62nd minute, assisting a goal in the 4–3 loss against
Tottenham Hotspur. On June 30, 2025, it was announced that she was departing the club upon the expiry of her contract. ==International career==