Markell played two very quiet years with the Cornwall Royals of the QMJHL before opting to jump to the American college route in 1975. It was still pretty uncommon for college players to make the NHL back then. Most players went to college more to get an education than to persue their NHL dreams. This was the case for Markell, though he never gave up on his dream.
Markell, perhaps a bit of a late bloomer, developed into a good goal scorer with a bit of a mean streak with Bowling Green of the CCHA. In 4 years he average just under 30 goals and about 60 points a year in the 40 game-or-so schedule. Those numbers caught the attention of the Winnipeg Jets, who signed Markell for their inaugural NHL season.
Markell had a pretty decent rookie year in 1979-80. The Jets were an absolutely terrible team, but Markell played admirably in the bad situation. He scored 10 goals and 17 points in 38 games, while splitting the season with the minor leagues. In the CHL where he spent the rest of the year with Tulsa, Markell played well, scoring 15 goals and 29 points in 35 contests.
Markell however had a tough time sticking in Winnipeg in 1980-81. This was due largely to the fact that he suffered from mononucleosis, and never fully recovered until after the end of the year.
Markell was involved in a big trade in the summer of 1981. He was basically a throw in as the Jets sent promising physical defenseman Scott Campbell to St. Louis for sharpshooting RW Paul McLean, defenseman Bryan Maxwell and backup goalie Ed Staniowski.
Blues GM Emile Francis called Markell "a 100 percent-er who can contend for a spot at left wing and will get a chance to make this club. I saw Markell at Bowling Green, and he can be a good goal scorer."
However Markell was quickly buried on the Blue's LW depth chart. Captain Brian Sutter was the team's top left wing, while scorers Jorgen Petterson and Perry Turnbull also held down spots. Spunky Jim Nill and defensive ace Ralph Klassen shared the 4th line role, leaving Markell in the minors.
Markell played the next three years with the Blues farm teams in the CHL. He developed each year into more of a scoring threat, and by 1983-84 he led the entire CHL in goal scoring with 44. He also finally got his chance to play with the Blues, appearing in just 2 games.
A free agent at the end of that season, Markell signed with the Minnesota North Stars organization, hoping to get a better chance to play. However things never worked out there either. Aside from one lonely game, Markell spent the entire injury troubled year in the American Hockey League.
Markell took a different direction starting in 1985-86, heading across the Atlantic to finish his hockey career.