Deputy Opposition Leader Rob Hulls is resigning after more than 15 years in State Parliament, paving the way for a by-election is his north-western seat of Niddrie.
The decision, to be announced at a press conference at 11 am today, follows a serious health scare for Mr Hulls last year that saw him placed in an induced coma after he realised he could not breathe.
At the time Mr Hulls, seen by some as the hardman of the Victorian Labor Party, promised to continue in Parliament.
Mr Hulls holds his seat by a 6.9 per cent margin.
A Labor source said there was no obvious successor to run for the seat.