A former Scotland U20 international, he made an instant impact at Doncaster with 13 tries in 27 appearances and was hailed as the best full back in the division by coach Brett Davey.
He has similarly impressed during his time with Leeds, being named Players' Player of the Season, and earning a place in the RFU Championship Dream XV, a team voted for by all the Championship coaches.
He also caught the eye of the national coaches this season, earning a call up to the Scotland squad for the 2013 Autumn internationals.
His consistently excellent performances for Leeds have made him a sought after commodity, and Nigel Davies is delighted to add him to his Gloucester squad for next season.
"Again, he's somebody who stands out at Championship level. Leeds are a good team, who play a particularly good brand of rugby and who are fighting hard to get into the Premiership.
"Steve's been a big part of their success. He's a very strong, very powerful runner from deep and who hits good lines. He was part of the Edinburgh Academy at one stage and moved to get more opportunities.
"As a result of playing in the Championship, he's gained a lot of experience and he's shown his quality.
"I'm very excited about this guy. Both he and Mark (Atkinson, announced earlier this week as signing from Bedford Blues) can make the step up from Championship level rugby and be a huge success.
"We're bringing really explosive players into the back line, who have got a big physical presence and that's important."
McColl will be following a similar path to Rob Cook. The former Cornish Pirate was a late addition to Gloucester's squad before the 2012-13 season and has gone on to become a first team regular.
"Rob was my first signing really, and we've been delighted with the way that he's made the step up. And we're confident that both these guys are going to do exactly the same
"They're coming in to a full time training environment and that, in itself, helps with these players. They'll be managed and looked after by our Medical and Strength and Conditioning staff and that will be hugely beneficial for them.
"They may not be as well known as some of the players we've announced in the past, but I'm very confident that they will have equally as big an impact."