Having lost out at the final hurdle in three previous seasons, O'Driscoll was delighted to win the title, particularly with several teammates set to depart in the summer including Ireland colleague Jonathan Sexton.
"It means an awful lot," said the 34-year-old centre, who this week signed a new 12-month deal with the Irish Rugby Football Union and Leinster and met with his Lions teammates today.
"Over the last three years we have gotten to the final hurdle and fallen so it is relief and great to send some of the boys off on a winning note and get the first double this club has had.
"Ulster have been the best side in the competition, that is why they finished first, and you only have to look at the scoreboard to see how tough it was.
"It's very hard when you have games the day before you are going to meet up (with the Lions).
"It is a big relief that everyone has come through unscathed and now it is something to really look forward to - seven weeks in Australia, it's great."