The presidential oath of office was administered to him by the Chief Justice Sophia Akuffo at an emergency sitting of the house on Sunday.
It follows the absence of the President, Nana Akufo-Addo and Vice President Dr Mahamudu Bawumia, from the country.
The president left Accra this Sunday after to attend the inauguration of George Weah as the President of Libeira.
Bawumia, who should have acted in his absence, is also on a medical leave in the UK after he took ill on Friday.
The President will return to Ghana on Tuesday