Allen is an established NHL goaltender but hockey isn't the only sport where he has had success. He was a two-time junior champion at the Kingswood Park Golf Course in his hometown of Fredericton, New Brunswick. The mental toughness required to thrive in golf could only have helped as he worked his way up through the hockey ranks.

Following his rookie season with St. John's of the Quebec Major Junior Hockey League, Allen helped Canada win a gold medal at the 2008 Under-18 World Championship. He also was named the tournament's MVP and top goaltender. Allen was selected by the St. Louis Blues in the second round (No. 34) of the 2008 NHL Draft.

Two years later Allen represented Canada at the IIHF World Junior Championship, where he won a silver medal, going 3-0 with two shutouts. Splitting the 2009-10 QMJHL season between Montreal and Drummondville, he was named to the league's First All-Star Team and won the Jacques Plante Trophy, given to the QMJHL goaltender with the best goals-against average (2.20). He was also the Canadian Hockey League Goaltender of the Year.

In 2010-11 Allen turned pro with Peoria of the American Hockey League and shared goaltending duties with another future NHL player, Ben Bishop. Allen had 25 wins in 47 games that season and was named the AHL Goaltender of the Month in November 2010 after going 6-1-0 with a 1.35 goals-against average, a .959 save percentage and three shutouts.

He played 38 games for Peoria in 2011-12 but did see his first NHL action that season with St. Louis on April 30, 2012, making a brief appearance in relief of Brian Elliott in Game 2 of the second round Stanley Cup Playoff series against the Los Angeles Kings. He got his first NHL win Feb. 12, 2013, against the Detroit Red Wings and was named to the NHL All-Rookie Team after leading first-year goalies in wins (nine) and GAA (2.46).

In 2013-14 with Chicago of the AHL, Allen became the first goalie since 1984-85 to lead the league in wins (33), GAA (2.03) and save percentage (.928) and was the top goaltender.

Allen won 22 games for the Blues in 2014-15 with a 2.28 GAA and .913 save percentage. He started all six playoff games for St. Louis. Still rookie-eligible, Allen earned the unique distinction of being named to the NHL All-Rookie Team for a second time.

Despite splitting time with Elliott in 2015-16, Allen tied for second in the NHL with six shutouts in 47 games (44 starts).

NOTES & TRANSACTIONS

• QMJHL First All-Star Team (2010)
• Canadian Major Junior First All-Star Team (2010)
• Canadian Major Junior Goaltender of the Year (2010)
• NHL All-Rookie Team (2013)
• AHL First All-Star Team (2014)
• Aldege "Baz" Bastien Award (AHL - Outstanding Goaltender) (2014)
• NHL All-Rookie Team (2015)
• Traded to Montreal by St. Louis with a 7th-round pick in 2022 NHL Draft for a 3rd-round pick and 7th-round pick in 2020 NHL Draft, September 2, 2020.