The opera singer had a life-saving operation to deal with the problem in October 2007, followed by a five-week radiotherapy course. It followed similar treatment on another brain tumour one year earlier.
"It was a tough old two or three years that I've had," said Watson, "but I'm feeling a lot better now - stronger and faster, maybe not better than I was before but getting there."
The singer added that he is planning to take part in the Bupa Great Manchester Run, a 10k run scheduled for May 17.
"I'm contemplating running at the event. It's going to be in the middle of my UK tour, so if I'm not somewhere down south or too far away I'd really like to do it. Recently I've started to get back into my fitness regime again and I'm enjoying it, so I'd like to."