The All Blacks legend recently met with Titans managing director Michael Searle, head coach John Cartwright and the club's medical staff to discuss the possibility of switching codes.
But the 31-year-old winger on Friday morning informed the Australian side of his decision to stay in union.
"We understand and respect the business decision Jonah has made and wish him all the best in rugby and in life," Searle said.
Lomu did not receive an offer from a Super 14 franchise to play in next season's southern hemisphere competition.
He admitted last month his dream of representing New Zealand at the 2007 World Cup in France was over.