MacKinnon is coming off a championship season where he led the Halifax Mooseheads to their first-ever Quebec Major Junior Hockey League title and first-ever Memorial Cup championship.
He was named most valuable player of the 2013 Memorial Cup after recording a tournament-high 13 points (seven goals, six assists) in only four games, which included a hat trick and five points in the final against Portland.
During the 2012-13 regular season, MacKinnon had 32 goals and 43 assists in 44 contests for Halifax, averaging 1.70 points-per-game. He finished tied for fourth on the Mooseheads in scoring and had a plus-40 rating.
MacKinnon went on to score 11 goals and add 22 assists in 17 playoff games as the Mooseheads won the QMJHL championship.
MacKinnon represented Canada at the 2013 world junior championship in Ufa, Russia. The six-foot, 182-pound centre appeared in all six of Canada's games at the tournament, posting one assist.
"The signing of this first NHL contract represents for me another step towards becoming a professional hockey player," the Halifax native said. "I am excited and thrilled to have been drafted by the Avalanche, and I am already working very hard in order to be ready physically and mentally for training camp."
MacKinnon was just the third 17-year-old drafted No. 1 overall in the last 26 years.