The pileup reported about 10:30 p.m. Christmas Eve involved five or six horses and four vehicles, the Suffolk Constabulary said in a release. Three of the horses died.
The crash occurred on the A14, a major road that runs from the port of Felixstowe on the Suffolk coast more than 100 miles west and connects to major routes. The highway was closed at Sproughton, near Ipswich, for several hours.
A 23-year-old Cambridgeshire man was taken to Ipswich Hospital in critical condition and died Tuesday afternoon, police said.
Another young man, a 26-year-old from Ipswich, was arrested on suspicion of causing danger to other drivers. He was quickly released on bail.
The Felixstowe Star said the dead man was in the first vehicle to hit the horses. A woman passenger was injured.
One of the horses killed was a pregnant mare.