2009-10: Conor Allen played for the USHL’s Sioux Falls Stampede . In 48 games he scored 7 goals with 8 assists and was +9 with 69 penalty minutes. The Stampede finished third in the West Conference and lost to Fargo in the first round of the playoffs. Allen missed the series due to an injury. In December he committed to playing college hockey at Massachusetts-Amherst in 2010-11.
2010-11: Allen played 31 games for Massachusetts-Amherst as a freshman. In a disappointing season for the Minutemen, who qualified for the Hockey East playoffs despite winning just six games, he spent much of the season partnered with fellow freshman Adam Phillips. Allen scored 2 goals with 4 assists and was -11 with 29 penalty minutes. UMass was swept by eventual national champion Boston College in the Hockey East quarterfinals.
2011-12: Allen skated in 35 of 36 games for Massachusetts-Amherst in his sophomore season. He scored 7 goals with 7 assists and was -1 with 28 penalty minutes. The Minutemen were tied for eighth with Northeastern but advanced to the Hockey East quarterfinals due to tiebreaker criteria and were again swept by Boston College in the Hockey East quarterfinals.
2012-13: Allen signed a two-year entry-level contract with the Rangers in March 2013 following his junior season at Massachusetts-Amherst. He played his first professional game with New York’s AHL affiliate in Connecticut and was -1 with no points nor penalty minutes in his only game with the Whale. Connecticut missed the AHL playoffs by two points despite finishing second in the Northeast Division. In 33 games for UMass as a junior, he scored 5 goals with 14 assists and was -1 with 53 penalty minutes. The Minutemen missed the Hockey East tournament after finishing ninth under first-year coach John Micheletto.
2013-14: Allen made his NHL debut with the Rangers in a December 29th game at Tampa Bay, appearing in three games with New York before being returned to AHL affiliate Hartford. He was -1 with no points nor penalties, averaging 14:26 minutes of ice time in his brief NHL stint. Allen scored 11 goals with 23 assists and was -4 with 71 penalty minutes in 72 regular season games for Hartford. The re-christened Wolfpack finished third in the Northeast Division, missing the AHL playoffs.
2014-15: Allen skated in four games with the Rangers in November, spending the bulk of his second pro season with New York AHL affiliate Hartford. He was -1 with no points and 4 penalty minutes playing for the Rangers. Allen scored 11 goals with 23 assists in 72 regular season games for the Wolfpack. He was +1 with 113 penalty minutes, trailing only Dylan McIlrath (165) for the team lead. Hartford finished first in the Northeast Division, advancing to the Eastern Conference finals in the playoffs. Allen scored 1 goal with 1 assist and was -4 with 10 penalty minutes in 12 playoff games. He signed a one-year contract with Nashville as an unrestricted free agent in July 2015.
Allen is a sound defender who has displayed both offensive instincts and toughness in his game at the NCAA and AHL levels. He is a reliable two-way defenseman with excellent vision and generally makes good decisions with and without the puck.
After signing with the Predators in the offseason, Allen has been dealt by the Nashville Predators to the Ottawa Senators in exchange for Patrick Mullen.