With Sydney's blessing, O'Riordan was part of the Tipperary side that defeated Cork by three points at Pairc Ui Chaoimh. Counties Kerry and Cork have shared every Munster title since 1923, except for Tipperary's most recent win in 1935 and a lone win by Clare in 1992.
The victory was extra special for the Tipperary side, as it came on the weekend that Ireland commemorated the 100th anniversary of the Bloody Sunday massacre at Croke Park.
"I can't put it into words. It's the best feeling I've had in many years," O'Riordan said on RTE Sport.
"It just fills me with pride so much and I get emotional even thinking about it, but it's one of the best days of my life and I'm just over the moon."