Marshall given Gloucestershire t20 captaincy
Marshall, the former New Zealand batsman, has scored 1,669 T20 runs in 72 innings and he also played three T20s for New Zealand before sacrificing his international career in 2007.
John Bracewell, Gloucestershire director of cricket, said: "Having Hamish at the helm will allow Alex Gidman an opportunity, in what has been an exceptionally busy start to the season, to freshen up and for the team to hear a new voice during this time."
Gidman has been Gloucestershire captain since taking over from Jon Lewis. He is closing in on 1,000 T20 runs but his side have failed to make any impression on the competition since reaching Finals Day for the second time in 2007 when they lost to Kent in the final at Edgbaston.
Gloucestershire's other appearance at Finals Day came at Trent Bridge in the inaugural year of T20 in 2003 where they lost to eventual winners Surrey in the semi-final: Gidman's 61 could not get his side home as they fell five runs short.
They also lost to Surrey in 2006 - the only other occasion where they have progressed out of the group stage - in a quarter-final at Bristol. They open their 2012 campaign against Somerset at Bristol on Thursday.
Their overseas player is former Sri Lanka spinner Muttiah Muralitharan but Kevin O'Brien, Gloucestershire's second overseas player from last season, has signed for Somerset.
O'Brien scored a 44-ball hundred in Gloucestershire's world-record domestic T20 score against Middlesex at last season, an innings where Marshall also scored a century from 53-balls. It was the first T20 innings in which two players have scored a century.
Alex Winter is an editorial assistant at ESPNcricinfo