[2] During the 2004–05 season, Varlamov made his debut on Lokomotiv's junior farm club, Lokomotiv-2, playing as backup to Ivan Kasutin in the 1st League (Russia 3).

His home debut in Washington came five days later on 18 December against the St. Louis Blues, where he made 29 saves on 31 shots and was named the second star of the game in a 4–2 Capitals win.

"[7] In Game 7 of that series, after allowing four early goals, he was pulled in favor of deposed starter José Théodore in which the Capitals were ultimately eliminated 6–2 by the eventual Stanley Cup champions.

[9] The start of the 2011–12 season proved successful for Varlamov and the Avalanche, but a disastrous November put the club back to the bottom of the Northwest Division.

Varlamov was often benched in favor of veteran backup Jean-Sébastien Giguère, originally brought in by the Avalanche to mentor the young Russian.

On 5 April 2012, the 81st game of the season, in a must-win situation for the Avalanche's playoff hopes, Varlamov made his career-high eighth consecutive start and let up four goals in a 5–2 loss against the last-placed Columbus Blue Jackets at Pepsi Center.

[10] Used as one of three main goaltenders on the Lokomotiv roster, Varlamov impressed early in his debut Kontinental Hockey League (KHL) season.

[11] Despite suffering a knee injury, Varlamov played in 16 games and led the KHL in GAA and save percentage before the conclusion of the NHL lockout called for his return to the Avalanche on 6 January 2013.

[25] On 1 May, Varlamov broke Chico Resch's record for the longest shutout streak in Islanders history, after shutting out the rival Rangers 3–0.

[34] Varlamov subsequently filed a civil suit against his girlfriend claiming abuse of process, and was awarded US$126,608 in damages for legal fees in 2016.

The correct pronunciation is var-LA-mov, similar to the syllable emphasis of the last names of fellow Russian netminders Evgeni Nabokov and Ilya Bryzgalov.

On 5 August 2009, Varlamov registered a change of spelling of his first name with the NHL, "for the upcoming season and foreseeable future," from the incorrect "Simeon" to "Semyon.

Backing up Anton Khudobin, Varlamov did not see much ice time, playing only in one game against Latvia, allowing one goal in a 3–1 round robin win.

He regained the starting position at the 2007 World Junior Championships and recorded a 1.51 GAA (second among tournament goalies to Carey Price of Canada) along with two shutouts.

Varlamov helped the Russians to the World Championships Final, where the team faced the Czech Republic, though Russia lost 2–1, earning the silver medal.

Varlamov played extremely well in Russia's net and was an important piece in the team that reached the World Championships Final, where they faced Slovakia.

At the 2013 IIHF World Championships, held in Finland and Sweden, Varlamov was Russia's second choice goaltender behind the Philadelphia Flyers' Ilya Bryzgalov, although both would play similar minutes throughout the tournament.

Bryzgalov was named the starter against the United States in the quarterfinals, where the U.S. crushed Russia 8–3 and ended their tournament, despite the inclusion of a star-studded roster that included Ilya Kovalchuk and Alexander Ovechkin, among others.