Head coach O'Connor has now been granted the necessary paperwork and will arrive in Leicester this week where he will have overall responsibility for playing matters.
"The opportunity to come back and be in charge at Leicester is phenomenal," said O'Connor, who won three Premiership titles in five years in his previous spell at the club before moving to Leinster in 2013.
"Leicester Tigers is certainly a place that I have very, very fond memories of and that I care about greatly."
O'Connor says it is important, too, to get down to work immediately with just two months left in the season.
"Having the chance to come in quickly and getting a look at the environment for the last couple of months of the season - right at what we hope is the business-end of the season - is a huge advantage from my perspective," he said.
"It's a chance to work with the squad and the staff, and that's a huge bonus before coming back and forming the plans for pre-season.
"There is also still a lot to play for this season and we know what we need to do."
Tigers resume their Aviva Premiership season with a trip to Twickenham to face Bath Rugby on Saturday and then have home games against Newcastle Falcons (Saturday, April 15) and Sale Sharks (Saturday, April 29) before the last-day trip to Worcester Warriors. For ticket advice on all remaining games, click here.