Jammeh announced the ban late on Monday during his annual tour of the country, Information Minister Sheriff Bojang said in a Facebook post. "(Jammeh) has declared in the last few minutes that FGM or female circumcision has been banned in The Gambia with immediate effect!!!" he wrote.
Anti-FGM campaigners, confirming the announcement, said it was not clear when a law would be passed to enable the ban to be enforced.
Seven out of nine ethnic groups in the predominantly Muslim country carry out FGM, an ancient ritual which is shrouded in secrecy and widely condemned elsewhere as a serious violation of women's rights.
The practice, which involves the removal of the external genitalia, causes numerous health problems which can be fatal. Some girls bleed to death or die from infections, while others die later in life from childbirth complications caused by FGM.
"President Jammeh's declaration sends a clear message to the world, but enacting a law urgently will send an even stronger signal," said anti-FGM activist Jaha Dukureh.
"A law is going to save countless lives in the Gambia."
One of the main challenges for activists in the Gambia has been tackling the misconception that FGM is a religious duty, but Dukureh said they had won the support of religious leaders, women's representatives and community elders in recent years.
FGM affects an estimated 140 million girls and women across a swathe of Africa and parts of the Middle East and Asia, and is seen by many families as a gateway to marriage and a way of preserving a girl's virginity. Uncut girls are often ostracised.
More than 1,000 communities and 150 cutters in the Gambia have abandoned FGM in four mass declarations since 2007, according to Isatou Touray, Gambia's highest-profile campaigner against FGM.
Her women's rights organisation GAMCOTRAP has organised the fifth "Dropping the Knife" declaration in the Central River Region on Nov. 25, the annual United Nations International Day for the Elimination of Violence Against Woman.
"The whole country has been calling for change and for a law - we are moving towards zero tolerance of FGM," said Touray, who has faced death threats during some 25 years of activism.
Nigeria outlawed FGM earlier this year, and the practice survives in only a few countries in the region, including Sierra Leone, Liberia and Mali.
Reporting by Tim Pearce, Thomson Reuters Foundation
