He was sworn-in about 5pm Senegalese time at the Gambian embassy in Dakar, Senegal.
A Photograph on his Twitter handle shows him taking the the oath of office.
He succeeds Alhaji Yahya Jammeh, who lost in the 1 December presidential election and has refused to vacate office when his term expired midnight yesterday.
“This is a victory of the Gambian nation. Our national flag will fly high among those of the most democratic nations of the world. #Gambia,” read a tweet after the ceremony.
Western ambassadors to Senegal, the UN envoy for West Africa and top officials from the regional bloc Ecowas (Economic Community of West African States) attended the ceremony, while hundreds of Gambian expatriates gathered outside the compound.
“I, Adama Barrow, do swear that I’ll well and truly prosecute the functions of office the president of the Republic of The Gambia. That I will preserve and defend the constitution,” he said.
In his inauguration speech, he ordered all members of The Gambia’s armed forces to remain in their barracks.
“Those found illegally holding arms will be considered rebels,” he warned.
West African military forces, stationed at the border, say they are ready to enforce a transfer of power in The Gambia, a popular beach destination among European holidaymakers.
Nigeria said on Thursday that its “armed reconnaissance air force are over Gambia”, the AFP reports.
“They have the capacity to strike,” Nigerian Air Force spokesman Ayodele Famuyiwa told the news agency.
Posted by Juliet Ekwebelam (NAN)