In an address on national radio late Monday night, Vieira also confirmed the departure of the ex-premier, Aristides Gomes.
Last month, Guinea-Bissau's parliament passed a motion to impeach Gomes, with 54 out of 85 parliamentarians voting in favor, saying a change was needed to pull the country out of its economic spiral. Prior to the vote, the country's three leading political parties had signed a pact saying Gomes' government needed to be replaced.
Gomes announced his resignation on March 29, but it was unclear if Vieira, a close ally of Gomes, would accept his resignation and name a new premier, as required by the country's constitution.
Vieira was elected last June in the first presidential vote since a 2003 military coup toppled democratically elected President Kumba Yala. He appointed his protege, Gomes, as prime minister, infuriating the PAIGC, which called the appointment unconstitutional.
Guinea-Bissau is deeply impoverished and has been wracked by coups since independence from Portugal in 1974.