Jammeh refused to step down after a December 1 election in which Barrow was declared the winner, triggering weeks of uncertainty that almost ended in a military intervention involving five other west African nations.
The longtime leader, wearing his habitual white flowing robes, waved to supporters before boarding a small, unmarked plane at Banjul airport alongside Guinea's President Alpha Conde after two days of talks over a departure deal.
"No legislative measures" would be taken that would infringe the "dignity, security, safety and rights" of Jammeh or his family, ECOWAS said in a joint declaration with the African Union and United Nations.
The departure opened the way for the transfer of power to Adama Barrow, who won the presidency seven weeks ago. Barrow, who was sworn in Thursday at Gambia's embassy in neighboring Senegal, was now expected to return home.
Yahya Jammeh has joined his fellow dictator Teodoro Obiang in Equatorial Guinea. Remember E/Guinea is not a signatory to the #ICC #Gambia— otsieli (@otsieli) January 22, 2017
Congratulations to the people of #Gambia on the departure of #Jammeh after 22 years in power. I wish Arab dictators would follow suit— Mohammad Ali Musawi (@malimusawi) January 22, 2017
#Gambia: Yahya #Jammeh arrives in his final destination of #Malabo, Equatorial #Guinea from Guinea #Conakry pic.twitter.com/53Dxm1RHWA— Alhagie Jobe (@freejobe39) January 22, 2017
#Gambia: Ex-Prez #Jammeh lands in Conakry.Heads to E/Guinea as final destination avoiding @IntlCrimCourt in future as country not signatory pic.twitter.com/ZjX89ucjf8— Alhagie Jobe (@freejobe39) January 22, 2017