Borussia Mönchengladbach[edit][]
On 10 March 2014, Sommer signed a five-year contract with German Bundesliga side Borussia Mönchengladbach, effective from 1 July. He was signed to replace Marc-André ter Stegen, who had joined Barcelona. In Sommer's first season at Mönchengladbach, 2014–15, Gladbach finished in third place in the Bundesliga, club's highest league finish since 1978. The club also managed to beat its record of consecutive matches without defeat, exceeding the record of 17 matches it had set during the 1970–71 season.
Sommer's debut came against Homburg in the DFB-Pokal, where Gladbach won 3–1. Sommer played against VfB Stuttgart on the opening day in a 1–1 draw. He was famously lobbed from long range by teammate Christoph Kramer against Borussia Dortmund in a 1–0 defeat, but Gladbach went on to secure qualification for the UEFA Champions League with one match remaining. At the season's conclusion, Sommer was named Gladbach's player of the season.
The 2015–16 season began poorly: Gladbach lost its opening match 4–0 to Borussia Dortmund, with Sommer being blamed for the first goal. The club was reported to be in large trouble, and before its first Champions League match of the season, the club's players held crisis talks to discuss their problems. After losing 3–0 to Sevilla, Sommer was heavily criticized for his play. After a fifth-straight Bundesliga defeat, against rivals 1. FC Köln, coach Lucien Favre resigned. In contrast to the previous year, it was the worst start to a season Gladbach had ever suffered.
Under new interim boss André Schubert, the club's dramatically improved with four wins from four matches, resulting in Schubert's permanent appointment. Sommer was forced to sit out against VfL Wolfsburg due to a broken nose, having injured it against Manchester City in the Champions League. He was replaced for the Wolfsburg match by Tobias Sippel. Sommer eventually played in all of the remaining Bundesliga matches, with his performances leading to interest from Manchester City.
However, Borussia Mönchengladbach finished fourth in the 2015–16 season, and qualified for the 2016–17 UEFA Champions League, in which they finished third in their group which had Barcelona, Manchester City and Celtic, then reached the Europa League round of 16, before being knocked out by Schalke 04 on the away goal rule after a 3–3 draw on aggregate.
In November 2019, Sommer extended his contract until 2023. In the 2020–21 UEFA Champions League, Borussia Mönchengladbach reached the round of 16, where they lost against Manchester City. On 27 August 2022, Sommer made 19 saves in a 1–1 away draw against Bayern Munich, to be a Bundesliga record.
Bayern Munich[edit][]
In December 2022, Bayern's longtime keeper Manuel Neuer suffered a lower leg fracture during a ski trip and was out until the end of the season, necessitating the signing of a replacement. On 19 January 2023, Sommer left Gladbach, having spent eight and a half years playing for Die Fohlen, and joined Bayern Munich on a contract until July 2025. He was sold for 8 million Euros. On 20 January, he made his debut for Bayern in a 1–1 away draw against RB Leipzig.
Inter Milan[edit][]
On 7 August 2023, Sommer joined Italian club Inter Milan, signing a contract until 2026. He was sold to Inter for 6.75 million Euros. Sommer won his first Derby della Madonnina against AC Milan, as Inter thrashed their rivals 5-1.