In April 2015, while playing for the Capitals, Grubauer became the first German-born goaltender to start and win a Stanley Cup playoff game.

Grubauer began his career in Germany, playing for his hometown's junior team, Starbulls Rosenheim, beginning in 2004 at the age of 13.

[5] Following the 2007–08 season, Grubauer moved to North America to play with the Belleville Bulls of the Ontario Hockey League (OHL) after being selected 25th overall in the 2008 CHL Import Draft.

[11] Grubauer signed a three-year, entry-level contract with the Washington Capitals on 4 October 2010 as his season with the Frontenacs began.

[12] Grubauer played 38 games with the Frontenacs, achieving a 22–13–3 record with a .903 save percentage and 3.62 GAA,[13] before falling ill with mononucleosis in February.

He reported that he had lost 20 pounds while ill.[15] Following training camp in September, Grubauer was assigned to the South Carolina Stingrays, the ECHL affiliate of the Capitals.

[23] A few days later, on 27 February 2013, Grubauer made his NHL debut with the Capitals in relief of Holtby in a 4–1 loss to the Philadelphia Flyers, stopping all 14 shots faced in just over 25 minutes of play.

[34] On 22 June 2018, Grubauer and Brooks Orpik were traded to the Colorado Avalanche in exchange for a 2018 second-round pick during the 2018 NHL Entry Draft.

[37] He helped lead the Avalanche to a first-round upset over the first-place Calgary Flames,[38] but lost in Round 2 to the San Jose Sharks in seven games.

[40] During the 2019 off-season, goaltender Semyon Varlamov signed a free-agent deal with the New York Islanders, cementing Grubauer's place as Colorado's starter.

With accomplished backup Pavel Francouz injured the entire season, Grubauer had a heavy workload and started 39 of 56 contests.

He finished the regular season with a record of 30–9–1, a GAA of 1.95, a save percentage of .922, and seven shutouts despite missing two weeks in April with a COVID-19 diagnosis.

[43] His win total was second only to Andrei Vasilevskiy (31) and his goals against average was second only to Alex Nedeljkovic (1.90), who played 17 fewer games than Grubauer.

Grubauer's save percentage was good for ninth on the season and he tied for the league lead in shutouts with Semyon Varlamov.

[45] The Avalanche won their division and the Presidents' Trophy for the third time in franchise history three days later after defeating the Los Angeles Kings 5–1 at home in the 56th and final game of the regular season.

[46] Grubauer continued his stellar play in the 2021 Stanley Cup playoffs as the Avalanche swept the St. Louis Blues in the West Division First Round[47] After defeating the Knights 3–2 in overtime in the second game of the second round and making a postseason career-high 39 saves, Grubauer became only the 10th goaltender in NHL history to record 10 or more consecutive victories in the postseason, joining elite company.

[48] On 28 July 2021, as a free agent and unable to come to terms with the Avalanche, Grubauer opted to sign a six-year, $35.4 million contract to join the new expansion club, the Seattle Kraken.

[50] He ended the Kraken's inaugural season with a 3.16 GAA and a .889 save percentage, making him one of the statistically worst starting goaltenders in the league.

[63] Three months following the 2008 U-17 Hockey Challenge, Grubauer, sharing goaltending duties with Felix Brückmann, played in the 2008 IIHF World U18 Championships, held in Kazan, Russia.

[65] Grubauer gained attention while competing for Germany in Division I of the 2010 World Junior Championships in Megève and Saint-Gervais-les-Bains, France.

Germany placed first in their group, winning all five of their games in order to put them back in the Top Division for the 2011 World Junior Championships.