The 34-year-old frontman scored 20 goals in 81 appearances for City during a three-year stay at Ashton Gate between 2010 and 2013.
He went on to spend time with AFC Bournemouth, Ipswich Town, Portsmouth and Swindon Town before returning to Bristol with a move to Rovers in July last year.
Pitman scored four goals in 18 games for Joey Barton’s side but was allowed to join National League club Eastleigh on loan for the remainder of the season in early February.
The veteran striker was released by Rovers at the end of the campaign and was believed to have interest from a number of clubs in the upper-tiers of the non-league game.
However, he has accepted an offer of a one-year deal with Hampshire-based AFC Portchester and will take on coaching duties with the Wessex League Premier Division club.
He told AFC Portchester’s official club website: “I’m really looking forward to it. Obviously for me it is something a little bit different coming out of full-time football but I’m really looking forward to it.
“It’s a really good set up here. I’m looking forward to getting started and hopefully having a successful year.
“It’s going to be different to what I’m used to but it is something I’m looking forward to and at this stage of my career it enables me to do some coaching as well, which is something I’m really looking forward to doing.
“I’ve had a good chat with the manager and the club want to win the league so I think that’s the aim - obviously it’s going to be difficult.
“On a personal level hopefully I can bring some experience and score a few goals.”