It was a double life, much of which has been revealed for the first time in his new book, Being Uncle Charlie.
Deasy says he wrote the book in part so his family and close friends would know what he was up to all those years.
"It was an incredibly hard period for them because they were literally in the dark about what I was doing," Deasy told CBC News.
His tenure included some close calls and notable busts — including a sting operation that led to an arrest and conviction in the stabbing death of a Nova Scotia store clerk.
The controversial "Mr. Big"-style sting saw Deasy elicit a confession from the killer while posing, with the aid of other undercover officers, as a crime boss.
He also describes his regrets, including the aftermath of a job in Montreal.
"A Montreal crime group was taken down ... and they thought they identified the person that introduced me," he recalled. The man was dragged out of his home, doused with gasoline, set on fire and shot.
"And it wasn't him at all," said Deasy.