|President Elect Barrow Adama of Gambia|
"Congratulations to president-elect Barrow Adama of Gambia," the Ghanaian president tweeted.
President Yahya Jammeh, who was defeated in Thursday’s poll, has called Mr Barrow to concede defeat.
"I'm calling you to wish you all the best. The Gambian people have spoken and I've no intentions to contest the will of almighty Allah," he told the president-elect on phone in the presence of the media after election results showed Mr Barrow had won.
"I wish you all the best, the country will be in your hands in January and you are assured of my guidance on your transition … but you have to work with me … so that I hand over the state house to you. … You are the elected president of The Gambia and I wish you all the best. I have no ill will and I wish you all the best. It is transparent; this is the will of Allah. … You have my full support," Mr Jammeh promised.
Mr Jammeh has led The Gambia for 22 years after he first took power in a coup in 1994.
The Gambia has not had a smooth power transfer since independence in 1965.
Electoral Commission chief Alieu Momar Njie said that Mr Barrow had won Thursday's election by more than 50,000 votes. He runs a property company which he founded in 2006.
A devout Muslim, Mr Jammeh, 51, once said he would rule for "one billion years" if "Allah willed it".
"It's really unique that someone who has been ruling this country for so long has accepted defeat," Mr Njie told reporters.
Mr Jammeh's defeat has been greeted with astonishment in The Gambia, where most people expected him to win. He has served four terms as president but now this unpredictable and ruthless man is to be replaced by a property developer.