The deal comes into effect for the 2014/15 football season.
32RED will have advertising on the Rangers shirts as well as “extensive visibility” at Ibrox, the club’s stadium, and across the club’s digital media platforms. It replaces a prior shirt sponsorship deal with current partner Blackthorn and Tennent Caledonian Breweries.
The value of the deal was not disclosed, though it is expected to give the club a financial boost.
"We are delighted to announce today a three-year shirt sponsorship deal with 32RED, the UK's premier online casino company,” said chief executive Graham Wallace.
"We look forward to working closely with them over the next three seasons in a partnership that we believe will be hugely beneficial to both parties.”
Rangers, one of the two ‘old firm’ football teams that have historically dominated Scottish football, has experienced a tumultuous few years as it has been rebuilding following the liquidation of the company that owned the club in 2012.
The assets of the football team were acquired by a new company from the liquidators, and the club’s finances were boosted by a subsequent IPO onto the AIM market in October 2012.
British billionaire Mike Ashley, majority shareholder of Sports Direct and owner of English football club Newcastle United, is among the significant shareholders in Rangers International Football Club, with a 4.6% stake.
As punishment for the liquidation the football team was relegated to the foot of the Scottish league system and is currently trying to gain successive promotions in order to return to the top flight.
Having won promotion in the last two seasons, Ranger’s will begin the 2014/15 season in The Championship, the second tier of the Scottish league system.