A state of emergency was originally declared in November 2015 following a suicide bomb attack on a bus.
This came after a series of deadly terror attacks, including the Sousse beach massacre.
Thirty Britons, all Tui holidaymakers, were shot dead on a beach at Port El Kantaoui in June 2015.
Another Briton, meanwhile, was killed in an attack on the Bardo Museum in Tunis three months earlier.
Prince Harry this week unveiled a memorial in Birmingham to the 31 victims.
The Foreign Office updated its travel advice to reflect the one-month extension on Thursday evening (March 7).
