Justin Andrew MacKinnon was charged with first degree murder in 2011, following a lengthy RCMP investigation into a double shooting that left Lisa Dudley, 37, and Guthrie MacKay, 33, dead in their home.
He was sentenced to seven years in prison minus time already served.
MacKinnon is the third man to plead guilty in the case. Co-accused Jack Woodruff, 53, was convicted on two counts of first-degree murder and was sentenced to life in prison without parole for 25 years.
Bruce Main, 66, also pleaded guilty to manslaughter and was sentenced to seven years in prison.
A fourth man, Tom Holden, 43, is currently awaiting trial for first-degree murder. Holden was released on bail in October.
The case made headlines when it was revealed that an RCMP officer was called to investigate the sound of gunshots at the house on the day of the murders, but never got out of his car. In a police review, he was later found guilty of disgraceful conduct and docked one day's pay.
It was later determined that McKay died instantly during the attack, but Dudley was left paralyzed after being tied to a chair and shot, but did not die until four days later while paramedics were transporting her to hospital.
A trial date for Holden, the fourth co-accused, has not been set.