Former Victorian premier Denis Napthine is to quit politics after 27 years in parliament.

It is understood he and Liberal colleague Terry Mulder will resign on Monday, triggering byelections in their electorates.

Napthine holds a 10.9% margin in South-West Coast, while Mulder has a 10.6% margin in Polwarth.

Napthine became Victorian premier in early 2013 after the surprise resignation of Ted Baillieu.

He led the Coalition to defeat in November 2014 and he resigned as Victorian Liberal party leader in favour of Matthew Guy on the night of the 2014 state election, which Labor won with a swing of more than 2%.

Napthine led the first one-term government to be defeated in Australia in 60 years.

“It is time for renewal, it is time for change,” he said at the time. “In the great tradition of Liberal, National party government, we leave the state in better condition than what we inherited only four years ago”.

Napthine and Mulder – a former roads and public transport minister – went to the backbench after the election defeat.

The former premier denied he planned to quit after the election and said he planned to see out his four-year term.

