Collins spent last season on loan at Burton Albion, making 40 appearances and keeping 11 clean sheets for the League One side. First team manager Michael Skubala said the signing added valuable competition to his goalkeeping options.
"It is important we have competition in the goalkeeper position and Brad will push all our goalkeepers," Skubala said.
"He has good experience and will add to the squad in a positive way."
Collins began his career at Chelsea, spending seven years in the academy, before loan and permanent spells with Forest Green Rovers and Barnsley took him through the lower divisions on his way to Coventry, where he made 43 appearances across two seasons before dropping out of the picture. Reflecting on his move to Ashton Gate, the goalkeeper said he felt he still had plenty to offer.
"I am delighted to be here," he said. "I feel like I have a lot to prove now to push on. I am a goalkeeper who likes to be on the front foot, likes to defend the space in behind and come for crosses. Every time I have played here it has been a great atmosphere and hopefully the good times are rolling on now."
Sporting director James Ellis said the club had moved quickly to bring in additional cover between the posts.
"It was important for us to get another goalkeeper in, and this is an excellent addition to the group," Ellis said. "Brad had a good season last campaign and he will bring his experience and hunger to push on every day. With Joe's situation becoming clear, we wanted to move quickly, and Pat and the recruitment team have done brilliantly to make that happen."
Collins joins a Bristol City squad preparing for the new Championship season and will provide senior competition within the goalkeeping department as the club continues to finalise its business ahead of the transfer window closing.
Having made well over 200 senior appearances across the Premier League, Championship and lower divisions during his career, Collins brings a level of durability that Skubala's coaching staff are expected to value as pre-season training intensifies.