Long serving Wellens, 30, who has made more than 375 appearances for the club, and Kiwi international Meli have signed two-year deals, with Flannery signing a one-year extension.
“It’s fair to say that all three have been integral to the Club’s success over the last few years,” Saints Chief Executive Tony Colquitt said. “Paul Wellens is playing at peak of form and is an integral part of the team. He leads by example and continues to be one of the best full backs in the business.
“We’re delighted to secure the services of Francis as he had plenty of opportunities both here and overseas. He had one of his most productive seasons to date and is an essential player at both wing and in the centres.”
He added: “Once again Chris has proved to be the consummate professional and we are pleased he is staying at the club. He had his best year for the Saints in 2010 and I’m sure he will want to improve on that next season.”