Former NSW Liberal premier Nick Greiner will stand down as iNSW chairman in July, with CEO Paul Broad set to leave in the near future.

Formed in July 2011, Infrastructure NSW was tasked with identifying much-needed upgrades to roads, rail and other projects crucial to the state, with the body publishing its state infrastructure plan in October.

NSW Premier Barry O'Farrell announced the departure of both men during Question Time on Thursday, describing iNSW's first two years as "nothing short of a success".

However, the surprise announcement has raised some suspicion, following media reports of tension between Broad and Transport NSW director general Les Wielinga.

News Ltd also reported that Greiner and Broad were unhappy with the pace of NSW government reforms.

Greiner dismissed this, stating that he had been planning to step down since February following the successful identification of five and 20-year modernisation plans.

"My decision is the right time in the organisation's five year cycle," he added.

Projects identified by iNSW include the proposed 33km WestConnex highway in Sydney's west and upgrades to the city's International Convention Exhibition Entertainment Precinct.

Former Victorian Secretary of Transport, Jim Betts, has been appointed iNSW's interim CEO, with O'Farrell planning to appoint former Business Council of Australia boss Graham Bradley as iNSW's next chairman.

Infrastructure Partnerships Australia welcomed the plan, reiterating that Greiner had done an outstanding job during his time as chairman.

"A transition is logical, as Infrastructure NSW moves from high level strategic planning into a nuts and bolts phase of advising government on the five year funded infrastructure program," IPA CEO Brendan Lyon said.

Broad will now take over as CEO of Snowy Hydro, an electricity generation and retail company headquartered in Cooma, NSW.