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-west suburban seat of Niddrie.

The decision, to be announced at a press conference at 11am 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.

Calling it quits ... Rob Hulls. Credit:Angela Milne

In mid-2011, the former deputy premier was rushed to hospital with a mystery illness that left him gasping for breath as his throat constricted.

He woke after five days in a coma-like state. Doctors identified the condition as epiglottitis - where a flap at the top of the windpipe swells, blocking the airways - and there were concerns the illness could return.