The surprise move is seen as an attempt by the Irish province to add some strength and experience to their back line with both Christian Cullen (shoulder) and Mike Mullins (Achilles tendon) currently suffering from long-term injuries.
South Africa Sevens international Anton Pitout has also been added to Munster's European Cup squad. The 28-year-old can play at centre and on the wing and joins from the Vodacom Cheetahs.
Connolly has signed a four-month contract with Declan Kidney's side and linked up with his team-mates on Friday afternoon in Limerick.
The 34-year-old came to fame in the 1990s with rugby league giants Wigan and St Helens and ended the 2005 season recently with relegated Super League club Widnes.
Last March, Munster secured the short-term signature of another thirty-something - Samoan legend Brian Lima - with a view to playing him in the European Cup, but a quadricep muscle injury prevented him from ever playing for the province.
Connolly has previously played rugby union for Harlequins (1996) and Orrell (2001, 2002) in an 18-year career.
It now remains to be seen what sort of role, if any, Connolly can play for Ireland's international rugby league side after he agreed last week to line out for them in next month's European Nations Championship.
The Irish, who lost to England in last year's final, are scheduled to face Scotland in Edinburgh on October 23 and Wales in Dublin on October 29 in Group One ties with a place in the November 5 final, in Carcassone, France, up for grabs.
Munster's European Cup Pool One campaign gets under way on October 21 with a visit to Sale's Edgeley Park and on October 29, the Irishmen entertain Castres at Thomond Park.