A London man has been sentenced to 20 years in prison for the beating of a 12-year-old autistic boy.

The sentence for 25-year-old Greg Simard was handed down in a London courtroom on Tuesday morning.

Simard had pleaded guilty earlier this year to four charges including attempted murder.

In her sentencing, Justice Jeanine LeRoy told the court that even though Simard suffers from a mental illness she did consider a life sentence.

She added "No sentence that I can impose will reflect...how [the victim] will spend the rest of his days."

The Crown had asked for a life sentence, while Simard's lawyer Gord Cudmore suggested a prison term of six to 10 years.

In court, Simard appeared to show remorse for the first time, telling the court "I'm ashamed of what I did, sorry for all the people I hurt. It's not who I am."

Outside the courthouse Cudmore said "I think that's true, that the person that committed this crime is not who Greg Simard is. I think the person who committed this crime is Greg Simard with a serious mental illness...This case is that's a tragedy no matter which side of the aisle you sit on."

The beating took place in September 2012, outside the Child and Parent Resource Institute (CPRI) in London, where Simard was a contract employee.

Simard has admitted he led the boy away from the facility and into a wooded area where he brutally beat him until he thought he was dead.

The child spent almost 200 days in hospital, receiving treatment for permanent brain damage and other severe injuries, and had re-learn how to eat and drink.

In June, Simard was found to be criminally responsible for the attack, after separate psychiatric assessments that produced conflicting opinions on his mental state.

Reacting to the sentencing decision, the boy's father says "If you look at the harm that was done to our son, there's no sentence that' s long enough. But we just need some closure and we need to put this behind us and get back to focussing on rehabilitating our son."

And while Simard will be eligible for parole after six years, he adds that his son's severe brain injuries will last much longer.

"This is not something that will ever change for us. We know that there is going to be lingering injury of some description forever."

With files from The Canadian Press