Former South Australian state MP and Lower House speaker Peter Lewis has died aged 75.

He served in the SA Lower House representing the Murray Mallee district between September 1979 and March 2006.

Mr Lewis was elected as a Liberal candidate but was expelled from the party in 2000, after speaking out against his own government and then-premier John Olsen.

He was re-elected in 2002 as an independent, and supported Labor to help it form government under Mike Rann, becoming speaker of the House of Assembly in return.

Labor has remained in power ever since, now under the leadership of Jay Weatherill.

Mr Lewis resigned from Parliament in 2006, after an outcry over threats to name an MP alleged to have been involved in child sexual abuse.

Mr Weatherill expressed his sympathies in Parliament on Thursday afternoon.

"I wish to extend my sympathies on behalf of the State Government to his family and friends," he said.

Deputy Premier John Rau said the controversial politician was an "engaging fellow".

"In my experience, my dealings with Peter personally, he was always very friendly," he said.

Deputy Liberal leader Vickie Chapman said the party would talk more about Mr Lewis during an upcoming condolence motion in Parliament.

"I just feel at this point it's a matter for the family to deal with and in due course the Parliament will of course consider this matter in a condolence motion."