The Tunisian Ennahda Movement appointed former Prime Minister Ali Laarayedh as new secretary-general succeeding Hamadi Jebali, the movement announced in a statement.
The statement said: "The Shura Council, the movement's top authority, decided during its regular meeting held on Saturday and Sunday to designate Ali Laarayedh as new secretary-general succeeding Hamadi Jebali who resigned earlier. The Council applauds the efforts of Hamadi Jebali as the head of the general secretariat and during all phases and will always remain in need of his leading role."
Jebali resigned in March stressing that his resignation did not "intend to divide or weaken the movement".
An official told AFP news agency that "Jebali has stepped down as secretary-general but has not left the movement".
Jebali served as Tunisia's prime minister in December 2011 after the first elections in Tunisia following the uprising which toppled President Zine El Abidine Ben Ali.
He presented his resignation following a political crisis which erupted over the assassination of opposition leader Chokri Belaid in February 2013.
It is widely believed that Laarayedh could run during the presidential elections scheduled at the end of the year.
Laarayedh served as chairman of the movement's Shura Council between 1983 and 1986 and then presided over its political bureau.
In 1992 he was sentenced to 15 years in prison where he was tortured under Ben Ali's regime.
The position of secretary-general had been vacant since Jebali announced his resignation in March.