Shane Hampson, 23, of Lime Grove, Skelmersdale, was convicted at Liverpool Crown Court last month of causing death by dangerous driving.
John Gregory, 49, from Wigan, Greater Manchester, died when the car crashed into the back of his vehicle in Skelmersdale, in February last year.
Hampson was also handed a four-year driving ban.
Police said Mr Gregory was driving his Chrysler Voyager home from work along Grimshaw Road when Hampson crashed into it from behind.
Mr Gregory's car overturned and he died at the scene.
Another car was also struck but the driver escaped unhurt.
Sgt Patrick Worden, from the Road Policing Unit, said: "I am very pleased with the sentence Hampson has been given and I hope this will serve as a warning to those who choose to behave in this manner - you will be punished.
"John Gregory was simply driving home from work when his car was struck from behind by a Volvo driven by Shane Hampson.
"As a result of the collision, the Chrysler overturned during which Mr Gregory was ejected from the car causing him significant injuries."
He added: "It was evident Hampson has been travelling at extremely high speed at the time of the collision and a lengthy investigation followed which identified that Hampson had driven dangerously not only at the time of the collision but within a few miles of the collision site.
"Despite claiming his innocence throughout, Hampson was convicted by a unanimous jury and I hope that this case sends out a strong message about the consequences of speeding."

Safety equipment had allegedly been bypassed on the Tangmere locomotive which meant it passed a signal at danger in Wiltshire earlier this year.
The legal proceedings have been brought by the Office of Rail and Road (ORR).
It said its investigation established a high-speed train had passed over the junction about a minute before.
Both West Coast Railway Company and the train driver have been charged under the Health and Safety at Work Act.
The driver has been charged over "alleged intentional misuse of the Train Protection and Warning System equipment", the ORR said.
The firm is facing similar charges, the office said, "on account of its alleged failure to implement managerial controls, procedures, training and monitoring to prevent staff turning off the TPWS equipment".
Both have been ordered to appear before Swindon magistrates in January.
Ian Prosser, HM Chief Inspector of Railways at the ORR, said: "The safety of staff, volunteers, passengers and members of the public is our absolute priority.
"Britain's railways have a good safety record. However, there have been a number of incidents over the past year involving West Coast Railway Company (WCRC) trains.
"The incident at Wootton Bassett junction, where a WCRC train passed a signal at danger, was caused by alleged intentional misuse of a key safety system. This could have easily led to a catastrophic train collision.
"ORR inspectors are working with the rail industry, in particular the mainline heritage sector, to ensure that lessons are learned, and public safety is not put at risk."
At the time of the incident, WCRC - which is based in Carnforth, Lancashire - was operating the steam train as a charter service.
A spokeswoman said "safety remains our paramount priority" and the firm had "worked hard to ensure that we have learned lessons to enhance our safety performance".
"At this time we have not received any papers from the ORR in relation to the prosecution and therefore we are unable to comment on the proceedings," she added.
A driver who caused a man's death when he crashed into the back of a car has been jailed for four years.
[NEXT_CONCEPT]
A steam train driver and their employer have been charged over a near miss in which a locomotive stopped across a busy main line railway junction.