A drink-driver who killed a Perth triathlete in a hit-and-run crash has been sentenced to five-and-a-half years' jail.

Joseph Francis Haenga, 38, was driving home after nightshift in October last year when he crashed into Brynt McSwain, 31, in Welshpool.

Mr McSwain was cycling home from his job as a firefighter at Perth Airport.

He was a champion triathlete.

Before the crash Haenga was speeding and swerving across lanes and narrowly missed hitting a truck.

After he hit Mr McSwain he did not stop.

Some distance away he crashed his car into a power pole and was arrested.

He then refused to provide a sample of his breath for analysis.

Haenga claimed he may have fallen asleep at the wheel because he had done a series of night shifts.

District Court Judge Richard Keen said the "only real explanation" for what happened was that Haenga was intoxicated because he had five alcoholic drinks after finishing his shift.

"In my view you were severely affected by alcohol," Judge Keen said.

Crime aggravated by failure to stop: judge

The court heard Haenga had a record of traffic offences in New Zealand but had not offended since coming to Australia a few years ago.

Judge Keen said the crime was aggravated by Haenga's failure to stop at the scene.

"It's not suggested you in any way could have saved Mr McSwain, but common humanity dictates you should have stopped and rendered assistance," he said.

Judge Keen said he also had to impose a sentence that deterred others from drink-driving.

"People are killed and maimed on a regular basis causing social harm in the community," he said.

"Word has to get out ... that those who are responsible cannot expect leniency."

Haenga will have to serve three-and-a-half years before he can be released.

Members of Mr McSwain's family, including his partner, were in court and cried throughout the sentencing hearing.

Outside court Haenga's lawyer Nicholas Scerri said his client and his family were extremely sorry for what had happened.

"Understandably they feel dreadful," he said.

"The McSwain family have lost a son and the Haenga family have lost the head of their house for five-and-a-half years.

"It's sad in every regard."