2009-10: Mark Alt attended Cretin-Derham High School in Minnesota. Scored 6 goals with 19 assists in 22 regular season games with 12 PIM. Added five assists in two Section 3AA games as Cretin-Derham defeated Eastview before falling, 2-1, to Woodbury, a team they had beaten earlier. Alt also played in the Upper Midwest High School Elite League with 1 assist in seven games for Team North East while at the same time playing quarterback for his high school football team. Invited to USA Hockey's 2010 junior evaluation camp in Lake Placid.
2010-11: Alt appeared in 35 of 36 games for the University of Minnesota as a freshman on a Gophers team that finished an uncharacteristic fifth in the WCHA. After assisting on the game-winning goal in his first game, an early season win over Massachusetts, Alt finished with 2 goals and 8 assists and was +3 with 22 PMs.
2011-12: Alt stepped into a leadership role for the University of Minnesota as a sophomore as part of a group of underclassmen defensemen who were key to the Gophers' first-place finish in the WCHA regular season. He played 43 games and was plus-18 with 5 goals and 17 assists and had 43 penalty minutes. The Gophers fell to North Dakota in the WCHA semifinals but avenged that loss in the NCAA West final to reach the Frozen Four.
2012-13: Alt signed a three-year entry-level contract with the Flyers in April of 2013 following his junior season at Minnesota and made his pro debut with Philadelphia's AHL affiliate in Adirondack. Obtained by the Flyers in January as part of the Brian Boucher trade, he skated in six games with the Phantoms, scoring 1 goal with 1 assist, and was -1 with 2 penalty minutes. Adirondack missed the playoffs after finishing last in the Northeast Division. The Gophers finished tied for first in the WCHA with St. Cloud State in what would be Alt's final season of college hockey. Partnered with freshman Mike Reilly (Columbus) for much of the season, Alt had 7 assists and was +18 with 20 penalty minutes in 39 games. Minnesota's season came to a disappointing ending with a loss to Colorado College in the WCHA semifinals and an overtime loss to eventual national champion Yale in the NCAA West Regional.
Alt was a two-sport star in high school, as he led Cretin-Derham to a state title as a quarterback in football. The son of former Kansas City Chiefs offensive lineman Jon Alt, he was entertaining offers to play football in college until late in the spring, when he committed to playing hockey at the University of Minnesota. Like his father, Alt is a tall man but despite his height is a fluid skater who has good speed and agility. Having not yet played at a higher level of hockey, he is still raw in terms of tactical play and positioning but is a strong two-way player according to scouts who've seen him play.
Alt's rights were dealt from the Carolina Hurricanes to the Philadelphia Flyers in January, 2013. Alt is playing for the Adirondack Phantoms of the AHL in 2013-14.