Colin Greening was born on March 9, 1986 St. John's Newfoundland. A graduate of the prestigious Cornell University, Greening was selected in the seventh round of the 2005 NHL Entry Draft by the Ottawa Senators.
Greenings made his professional debut in the American Hockey League with the Binghamton Senators in 2010 and shortly thereafter received his first taste of NHL action. He graduated to the NHL in February 2011 and scored his first goal on March 3 in a Senators victory over the Atlanta Thrashers.
In 2011-12, Greening would appear in all 82 games for the Senators, recording 17 goals and 20 assists, while providing the young Senators club with solid two-way play. With the NHL locked out to start the following season, Greening would begin the year with the Aalborg Pirates in Denmark. When play resumed at the NHL level, Greening would see action in 47 games, scoring eight times and adding 11 assists.
Greening's offensive numbers would dip in 2013-14. In 76 games for the Senators he scored just six times and added 11 assists. The following year he would struggle to remain in the Sens lineup and even spent time in the American Hockey League.
On February 9th, 2016, Greening's time in the Senators organization would come to an end. He was traded to the Toronto Maple Leafs in a nine-player deal which saw Dion Phaneuf going to the Ottawa Senators. Greening would make his Leafs debut two days later against the Edmonton Oilers.