The 36-years-old Minesh Parbat was driving at 60 mph when the crash took place in West Sussex, on March 9, 2014.
His girlfriend, Lisa Watling, 28, was thrown from the car and died later in hospital from her injuries. Parbat, who denied causing her death was found guilty after a trial in July, reported BBC.
He had claimed in court he dropped his trousers as part of a dare with mother-of-two Watling.
He told jurors she said she was feeling "horny" and invited him to pull down his trousers as he drove.
He claimed she sat on the dashboard, then moved in front of him and obscured his view.
But he denied anything sexual had taken place and said he struggled to get Watling off him before the crash.