David slept in a carpark stairwell to escape the cold on Christmas. The homeless father was then arrested in a move that has sparked outrage

A homeless father was arrested after heading out looking for a warm place to sleep at Christmas, in what has been portrayed as an attempt to 'criminalise' the disadvantaged.

David Evans, 57, slept in the covered car park on Frome Street, in Adelaide's CBD, to escape the 13ºC weather on Saturday and the following night on Christmas Eve.

He was arrested and charged with trespassing before spending Christmas Day behind bars.

Evans faced an uphill legal battle until Mary Shaw KC, South Australia's top lawyer, stepped in to help him and his charges were successfully dropped.

Ms Shaw was far from happy with the overall experience, claiming it was an attempt to 'criminalise' homelessness in the state.

Topside Mary Shaw KC (right) has come to the aid of a homeless father, David Evans (left), who spent Christmas in jail on trespassing charges while trying to find shelter on a cold night

She said she will lobby SA Attorney General Kyam Maher to keep homeless people out of jail and find alternatives.

“Our services would be better spent on those who really deserve to be in prison, and not on people like Mr Evans,” Ms Shaw told 7News.

She is considered one of the state's top brass after being appointed lead defense lawyer in the Snowtown murders case, Australia's worst serial killing.

Ms Shaw came to Mr Evans' defense 18 years after he first met him.

At the time she was a judge and Mr Evans came to court after he started using heroin.

Rather than send Mr. Evans to jail, Ms. Shaw ordered him to see a doctor to get pain medication and help him come off the drug.

Ms Shaw first met Mr Evans 18 years ago when she was a judge, and ordered the then-heroin user to seek help from a doctor rather than send him to prison

Ms Shaw first met Mr Evans 18 years ago when she was a judge, and ordered the then-heroin user to seek help from a doctor rather than send him to prison

Mr Evans would later write to Mrs Shaw to thank her for her kindness and clemency in helping him bring his family back together.

“It brought me back together with my family, with my son,” Mr Evans told 7NEWS.

“He was just a little guy at the time, five or six, and it meant a lot to him.”

Although it is likely he will have to sleep on the streets again, Ms Shaw took the opportunity to present him with a new pair of shoes outside court.