The two men who died have not been named by police but were aged 22 and 24 and both were from east London.
Two other passengers in the same car were also hurt and taken to St Mary's Hospital in Paddington, central London, with "serious injuries", Hertfordshire Police said.
Four men travelling in the other BMW also needed hospital treatment for their injuries.
The accident, which happened between junctions five and four, resulted in the closure of five junctions of the motorway in both directions, and the southbound stretch was shut for several hours.
Hertfordshire Police have appealed for witnesses to the crash or the events that led up to it to contact them.
More top news
A man from north London has been jailed for 27 years for owning guns and conspiring to supply drugs. Two others were also jailed.
One of the country's most extravagant private homes has been snapped up for just a quarter of the original £100 million asking price
Transport for London is being forced to pull down Germanwings tube adverts with the words "get ready to be surprised" after the fatal crash