The Italian rider won in a time of 5:50.02 on a wet and misty course that wreaked havoc with the field.
A leading group of ten riders - Trentin (ITA), Van Aert (BEL), Van der Poel (NED), Maurits Lammertink (NED), Davide Cimolai (ITA), Emils Liepins (LAT), Xandro Meurisse (BEL), Nico Denz (GER), Michael Albasini (SUI) and Pierre Luc Perichon (FRA) – looked set to contest a sprint finish.
Disaster as four riders crash in the road race
However, the slippery conditions whittled down the break of 10 to five with 9.5km to go after Lammertink skidded into a barrier, leaving Italy with two riders - Cimolai and Trentin - in the front pack.
Cimolai led out Trentin perfectly for the Mitchelton–Scott rider to claim the white, blue and gold jersey.
"I was not in good shape and I still have a lot of pain from my crash at the Tour De France a few weeks ago," said Trentin.
"It was a very technical course and it was really hard. In the end, I still felt a lot of pain in my back and in my hip. I think I really needed more time to recover for this race."
Trentin sprints to European road race glory
Victory for the 29-year-old Italian is all the more remarkable considering that Trentin suffered a spinal fracture at Paris-Roubaix in April, and means Italy secure the double in the road race after Marta Bastianelli took a convincing sprint victory ahead of defending champion Marianne Vos in the women’s race.
World champion Sagan abandons road race in Glasgow
Trentin follows previous European champions, Peter Sagan (2016) - who abandoned - and Alexander Kristoff (2017), while the tough conditions saw cyclo-cross stars Van der Poel and Van Aert emerge to take silver and bronze.