In the first half of the 2010–11 Season, ter Stegen established himself as the star of Borussia Mönchengladbach's reserve team and was frequently seen on the first-team bench. Whilst he was enjoying a relatively successful season, the same could not be said for his first-team colleagues. Mönchengladbach's senior side were seemingly failing in their efforts to avoid relegation, and on 14 February 2011, then-manager Michael Frontzeck was replaced by Lucien Favre, with the team rooted to the bottom of the Bundesliga, having accumulated only 16 points after 22 match days.
Results soon improved, but the erratic form of first-choice goalkeeper Logan Bailly held the team back. Whilst he was able to produce match-winning performances such as the one against Werder Bremen, these were few and far between, and were frequently cancelled out by uninspiring games. The fans of Die Fohlen were quick to discredit the Belgian international, with some accusing him of putting more effort into his modelling career than his football. Ter Stegen's progress for the reserve team had not gone unnoticed by the supporters, and the new manager was inundated with demands to start the young prodigy in the league. Favre eventually lost patience with Bailly, and on 10 April 2011, relegated him to the bench in favour of Ter Stegen for the match against 1. FC Köln. The young German did not disappoint, and the defence boasted a previously unseen solidity. He kept his place in the team for the remainder of the season, keeping four clean-sheets out of a possible five in the last five matchdays as Mönchengladbach avoided relegation via the playoffs. During this run, he shot to prominence with a last-man-standing display against eventual champions Borussia Dortmund, making a string of world-class saves as Die Fohlen secured a famous 1–0 victory.
Ter Stegen's status as first-choice goalkeeper was cemented when Bailly was sent on loan to Swiss side Neuchâtel Xamax and the no.1 shirt delegated to ter Stegen, who had previously worn 21.
During the summer transfer window, Bayern Munich had succeeded in their drawn-out pursuit of Schalke 04's captain Manuel Neuer. The German international made his debut against ter Stegen's Mönchengladbach at the Allianz Arena. The game did not go the way the pundits predicted, however, with ter Stegen producing yet another inspired display whilst his counterpart Neuer made the error that condemned Bayern to a 1–0 defeat. Following this game, Borussia Mönchengladbach embarked on an unlikely title challenge, with ter Stegen and fellow youngster Marco Reus providing the inspiration for Die Fohlen.
Ter Stegen was rewarded for his performances by Joachim Löw, who called him up to Germany's provisional squad for UEFA Euro 2012. He made his debut on 26 May 2012, in the 5–3 loss against Switzerland in a friendly match, but did not make the final cut for the tournament. He stopped a penalty from Messi in his second international match in the 1–3 loss against Argentina. He was called up to Germany's tour on America in May/June 2013. On 2 June, against USA, he failed to control the ball after a back pass from Benedikt Höwedes which gifted USA with a goal. The game ended 4–3 to the USA. In the three matches that he played for Germany the team never won and they conceded 12 goals.