The centre will join Danny Wilson's playing group on a full-time basis in January 2022, splitting his time in the interim between the club and his Team GB and Scotland 7s commitments.
It will be for a third spell in Glasgow colours for the midfield man, having made his club debut off the bench in the opening match of the 2015/16 season against the Scarlets at Scotstoun.
Having come through the ranks at Ayr, the 28-year-old made his first Glasgow Warriors appearance in five years when selected for last November's trip to Ulster, capping the occasion by being named in the Guinness PRO14 Team of the Round.
His most recent outing for the club came back in March, playing a key role in a 46-25 home victory over Benetton.
Fergusson returns to the Warriors after earning selection for the Olympic Games in Tokyo earlier this year, one of four Scottish representatives in the 13-strong travelling squad.
A try in a 24-0 victory over Canada was one of a series of standout moments in Fergusson's four appearances at the tournament, helping Great Britain to a fourth-place finish.
Having also represented Scotland at the 2018 Commonwealth Games on Australia's Gold Coast, he recently helped Team GB to back-to-back podium finishes at the World Sevens Series events in Vancouver and Edmonton.
Away from his playing career, Fergusson is a keen charity campaigner after overcoming Hodgkin's Lymphoma at the age of 20, and is serving as Ayr's assistant coach for the 2021/22 Tennent's National League campaign.
The centre told glasgowwarriors.org: "I'm buzzing to have signed for the club.
"I came through the Glasgow academy, and it's always been a lifelong rugby dream to sign for Glasgow.
"My family are here, and Glasgow has been my home club and the club I've supported since I was a boy so it was a really easy decision for me when the offer of a contract came through.
"I'm looking forward to continuing to play for GB7s up until the New Year and then pivoting to focus all of my attention on Glasgow and hopefully trying to get myself back in a Warriors jersey.
"I just want to play as much rugby as possible and this contract is going to allow me to do just that.
"I'm just buzzing to be back - I've not had the chance to play in front of the Scotstoun crowd in nearly seven years, and I'm looking forward to pushing for my place in the 23 and to run out in front of my friends and family at Scotstoun."
Glasgow Warriors Head Coach Danny Wilson welcomed the news, adding: "Robbie played really well for us last season and took his opportunities when they came.
"We were all pleased to see him earn his spot in the GB7s squad for the Olympics and more recently the 2021 World 7s Series.
"Robbie is a quality player, a strong leader, a great communicator, and a poplar member of our squad. We're looking forward to having him back in environment and competing for the jersey."