The Perth-based firm said it was buying £82m worth of new vehicles for its regional networks in England, Scotland and Wales.
A further £10m will be invested in new buses for London and about £4.5m in coaches for its megabus.com operations.
Falkirk-headquartered coach maker Alexander Dennis (ADL) will produce 415 of the new vehicles.
Most of the rest will be made by Volvo and Mercedes Benz.
The new fleet will be introduced in the 2016-17 financial year.
Stagecoach said it had now invested more than £1bn in new buses and coaches since 2006-07.
All of the new vehicles will be built to meet Euro 6 emissions standards. Most will also have wifi installed.
The orders include 280 low-floor double-decker vehicles and nearly 100 single decker and midi vehicles.
Stagecoach chief executive Martin Griffiths said: "We are investing in state-of-the-art, cleaner, greener vehicles, digital technology and smart ticketing to raise the bar and deliver an even higher standard of service.
"These latest vehicle orders are an important part of our strategy to encourage even more people to take the bus."
Transport group Stagecoach has placed orders for about 480 buses and coaches in deals worth a total of £97m.