Malcolm Turnbull has formally resigned his seat, as his successor Scott Morrison paid tribute to him as a prime minister who delivered some "very big things".

Mr Turnbull, who first entered parliament in 2004, on Friday confirmed his resignation from the NSW seat of Wentworth in writing to Speaker Tony Smith.

Having stepped down from the Liberal leadership in the wake of Peter Dutton's challenge, Mr Turnbull declared it was best that former prime ministers do not stick around parliament.

Malcolm Turnbull waves goodbye at the end of his final press conference as prime minister, surrounded by granddaughter Alice and grandson Jack. Credit:Alex Ellinghausen

The Wentworth byelection, which is expected to be held in October, will be hotly contested both in terms of Liberal Party preselection and the poll itself.