They will essentially job-share the role from May 10, with Mr Jenas working Mondays to Wednesdays, while Mr Keating will host Thursdays and Fridays.
The two men have been standing in as hosts on the BBC teatime show since Matt Baker left a year ago.
Mr Jenas, who played professional football with Tottenham Hotspur and England before becoming a pundit, said he was “really looking forward to joining as a full time host alongside Ronan”.
Mr Keating, who will continue to co-present the Magic Radio breakfast show, added that he was “so delighted to officially be a part of The One Show family”.
The One Show editor Rob Unsworth said: “We're thrilled to have Ronan and Jermaine join us as the regular One Show hosts alongside Alex on the sofa.
“It's an exciting new chapter for the show, and we're looking forward to viewers getting to know a different side to such well-known faces.”
Others including Alex Scott and Amol Rajan will continue to fill in when required, with the BBC confirming the programme's “extended family of presenters” would still co-host episodes.
Last month, Jones revealed on air that she is expecting her third baby but no decision has been made on who will fill in her role as maternity cover.