The modern fleet will include enhanced wi-fi, digital customer information screens and onboard air conditioning.
It will also be fuelled with recycled vegetable oil, which Chiltern said would help reduce emissions.
Sean Woodcock, MP for Banbury – which has a station on the Chiltern line, said he was “delighted” by Tuesday’s announcement.
He said the standard of Chiltern trains had been a “regular complaint of constituents throughout” his first year in office.
“I am pleased that this happened and that better and more comfortable journeys are imminent,” he added.
Rail Minister Lord Hendy said the investment showed “this government is putting passengers back at the heart of the 21st Century railway”.
“We are continuing to support Chiltern as they develop a plan to introduce additional services into their timetable, giving people more opportunities to work, live, and socialise,” he said.