Mr Knoll, who was transport minister until he resigned from the Liberal cabinet earlier this year, says the past six months have been some of the most difficult he has experienced and have put a significant strain on his mental health.

But he says he was proud of his work as a regional member of parliament and as a minister.

"In taking on the roles I have held, it is inevitable that sacrifices were made by those closest to me in order to enable me to devote the time and energy to the enormous task my ministerial workload demanded," Mr Knoll said in a statement on Tuesday.

"This means at times I wasn't able to be present as a father, husband, brother, son and friend.

"I have a choice to become either a better politician or a better person to those closest to me.

"I am choosing the latter."

Mr Knoll was first elected to parliament in 2014 as the member of Schubert which takes in the Barossa Valley, north of Adelaide.

He was seen by some in the Liberal Party as a future treasurer and potential leader.

But his time as minister was troubled with the government forced to back down on a number of decisions related to his portfolio including plans to axe some bus services in Adelaide.

He then quit as a minister earlier this year when it was revealed he, and a number of other country MPs, had possibly made mistakes in claiming an accommodation allowance available to country MPs.

Mr Knoll paid back several thousand dollars.

Premier Steven Marshall said he was disappointed Mr Knoll would not continue in parliament but understood and respected his decision.

"The pressures of service are great and they are increasing," Mr Marshall said.

"I thank him for his service to cabinet and to his electorate."

Australian Associated Press