Mr. Tambuwal decamped after months of speculation. He had previously denied he was moving to the APC despite openly associating with the party.
The clearest indication he was joining theparty came more than a week ago when he attended a meeting of the APC in Sokoto State.
He said the state governor, Aliyu Wammako, had invited him for the meeting after he was snubbed by a visiting PDP delegation to the state, led by Tony Anenih, the Board of Trustees chairman.
His months of denial is believed to have been informed by his concerns about losing his position as the speaker.
The PDP said its National Working Committee has met with its leaders in the House of Representatives concerning the defection of the speaker, and after due considerations.
It said the speaker should do what is honourable since his new party is in the minority.
“After a thorough consideration of the matter, the NWC came to a conclusion that the Hon. Speaker, as a responsible elected officer, knows full well what is needful and honourable of him since his new party is in the minority,” a statement by the party’s publicity secretary, Olisa Metuh, said.
“We are not unmindful of the fact that Hon. Tambuwal became Speaker on the platform of the PDP as the political party with the majority of seats in the House of Representatives and that this incontrovertible fact has not changed.”