The driver diverted the Peterborough to London Kings Cross service to Huntingdon to protect passengers after a knifeman attacked them Saturday evening.
Armed officers and paramedics boarded the Huntingdon-bound service within minutes and arrested two suspects within eight minutes of the 999 call.
The driver, an Iraq War veteran and former Royal Navy chief petty officer, coordinated with signallers to divert the train and safeguard passengers.