After replacing Michal Neuvirth with ten minutes remaining and the game tied 3–3, Holtby stopped four Bruins shots as the Capitals scored two goals to give him the win.

[7] Holtby started Game 1 of the 2012 playoffs against the defending Stanley Cup champion and second-seeded Boston Bruins, saving 29 of 30 shots in a 1–0 overtime loss.

One minute and 32 seconds into the game, Brad Richards of the Rangers blasted a slap shot past Holtby, making the score 1–0 early in.

After his impressive playoff performances as a rookie, Holtby was rewarded with the starting goaltender's job for the 2012–13 season, as named by Washington's new head coach, Adam Oates.

The Washington Capitals made him a qualifying offer to retain his NHL rights and, on July 5, 2015, Holtby filed for Salary Arbitration.

Capitals' head coach Barry Trotz opted to choose back-up goaltender Philipp Grubauer to start the 2018 playoffs.

[21] After Grubauer struggled against the seventh-seeded Columbus Blue Jackets in the first two games, Holtby stepped in as the Capitals starting goaltender, not being pulled for the remainder of the playoffs.

Holtby helped to lead the Capitals to their first Stanley Cup in franchise history, posting a record of 16–7, a .922 save percentage, a 2.16 goals against average and two consecutive shutouts against the top-seeded Tampa Bay Lightning in the Eastern Conference Finals.

Holtby is remembered for a play during Game 2 of the 2018 Stanley Cup Finals, in which he made a sprawling stick save on an open-net shot by Vegas Golden Knights forward Alex Tuch.

Holtby was exposed by the Canucks in the 2021 NHL Expansion Draft and, after going unclaimed, he was placed on unconditional waivers for the purpose of buying out the final year of his contract on July 27, 2021.

Holtby and his wife Brandi (née Bodnar) have two children and resided in Alexandria, Virginia, for the 10 years he played for Washington.

[31][36] During their move to Vancouver, Holtby was stopped at the border by Federal Fish and Wildlife due to missing paperwork that would allow the family's two pet tortoises, Honey and Maple, to cross into Canada.

[41][42][43] He credits his dedication to LGBTQ+ issues to stumbling upon a Human Rights Campaign (HRC) Action Center housed in Harvey Milk's home in San Francisco while on his honeymoon.

[46][45] He was one of three Capitals players (the others being Brett Connolly and Devante Smith-Pelly) who declined to visit the White House during the Trump administration after winning the Stanley Cup, an NHL tradition, saying he needed to "stay true to [his] values.

"[47][48] Following the murder of George Floyd and the subsequent protests, Holtby posted on Twitter for the first time in three years to show his support for the Black Lives Matter movement, recognizing himself as someone in the "white privileged category," and urging others to speak up.

[49] He and his wife held an auction during the summer of 2020 and raised nearly $40,000 for Black Lives Matter DC and the Leadership Conference on Civil and Human Rights.

[52] Gunnarson and Coast Salish artist Luke Marston collaborated on his new mask, which featured the legend of the Gonakadet, or Sea-Wolf, which stresses the importance of family units traveling and hunting together.