Lomani moved to Saints from Australian side Melbourne Rebels last summer but he has only been able to make five appearances for the club, all of which came from the bench.
Alex Mitchell has kept hold of the No.9 shirt for most of the campaign, with Tom James often the preferred back up.
The 25-year-old has been linked with a return to Fiji to play for the new Super Rugby side, Fijian Drua.
A Saints statement read: "Northampton Saints can today confirm that scrum-half Frank Lomani has been released from his contract with the club to pursue another playing opportunity overseas.
"The Fijian No.9 arrived at cinch Stadium at Franklin’s Gardens last summer ahead of the 2021/22 campaign, and made five appearances in black, green and gold.
"The club would like to thank Frank for his contribution to Northampton Saints and to wish him well for the future."