Marsch, a former U.S. international, played 14 seasons as a midfielder for three Major League Soccer teams, winning the U.S. Open cup four times, three MLS Cup titles, and the Supporters Shield once.

His coaching journey began in 2010 as an assistant coach on Bob Bradley’s staff that helped the United States Men’s National Team reach the last 16 of the 2010 FIFA World Cup in South Africa.

Marsch started his relationship with Canadian soccer in 2012 when he was named the inaugural manager of the 19th MLS expansion franchise, the Montreal Impact (now CF Montréal). ​ In 2015, he assumed the head coaching role at New York Red Bulls and led the club to the MLS Supporters' Shield with a club record 18 league victories. Marsch was named the MLS Coach of the Year. Marsch remains the New York Red Bulls most successful manager in their history, with 76 victories.

In 2018, Marsch’s journey with the Red Bull soccer group continued as he left New York to join RB Leipzig in Germany’s Bundesliga as assistant manager to Ralph Rangnick. After a successful 2018/19 season with Leipzig that saw a third-placed finish in the Bundesliga, a cup final appearance, and the club competing in the UEFA Europa League, he departed to join his third club within the Red Bull multi-club network as the manager of FC Red Bull Salzburg of the Austrian Bundesliga. After he joined in the summer of ​ 2019, Marsch’s impact at Salzburg was immediate and he led the club to a league and cup double in both of his seasons in charge as manager. This made him the first American head coach to win a top-flight league title in Europe. The league championships brought UEFA Champions League qualification, and Marsch’s legacy was cemented with Salzburg fans when he led the team to a 6-2 victory against KRC Genk in their first-ever group stage match.

Marsch re-joined RB Leipzig in 2021, this time as manager. He successfully guided them to qualify for the UEFA Champions League through the play-off round. They subsequently finished third in their group, qualifying for the UEFA Europa League knockout stages. ​ He departed the club in December 2021, and it wasn’t long before he embarked on the next stage of a football journey that has seen him coach in 5 countries to date.

Marsch joined Leeds United in England’s Premier League in February 2022, and he guided them to safety from relegation in the 2022/23 season with a final-day win at Brentford. This victory saw Leeds become the only club to escape relegation when entering the final day of the season in the league’s bottom three teams. He then oversaw the club’s summer 2022 transfer window, where club record transfer sales were achieved. ​ His departure came at a time when the club sat in 12th in the Premier League for non-penalty expected goals, and the club led the league in disruption of opposition passes by a large margin.

In total, Marsch has coached 339 matches, boasting a 170-66-103 record across his managerial career, and becomes the 20th head coach in Canada Soccer’s Men’s National Team history.