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."

Edward Alexander Lee, 34, was sentenced to three years on probation at Belfast Crown Court on Wednesday.
Judge Gordon Kerr QC said it was the best way of protecting society and helping Lee to change his ways.
Lee, originally from Whitehall Square, Belfast, but now living in England, pleaded guilty to a total of 15 charges related to child pornography.
The court was told the vast majority of the images were in the lowest categories, although some were in the higher - more serious - categories.
Lee was described by his wife as a being "loving and normal young man".
Judge Kerr said that while he had viewed the images for his "own strange pleasure", they were serious matters as "children were abused for these images to be made".
He added that children would continue to be abused while people like Lee continued to view such material, and that "society would not tolerate such behaviour".
Judge Kerr said a sentence of up to a year in prison would do very little to assist Lee or the community.
Placing him on probation, he ordered him to complete a course on sexual offending to help him stop viewing such images.
Earlier, prosecutor Simon Jenkins said that when police went to Lee's then Belfast home on 5 June, 2014, he immediately confirmed he was the man they were looking for.
On computer equipment seized, police uncovered a number of folders, which Lee admitted creating.
During interview, Lee said that he had been downloading images "for perhaps the last nine years".
Defence lawyer Taylor Campbell said that Lee had admitted his guilt from the outset, pleading guilty at arraignment, and was entirely frank and co-operative with police.

Australian businessman David Prior said he hoped to double production at Bladnoch Distillery, near Wigtown.
The single malt will be relaunched and he also has plans to introduce a new blend called Pure Scot.
Mr Prior said it would be aimed at a new generation of whisky drinkers in his homeland and hoped it would have a considerable local economic impact.
"I think there's some great things happening in other parts of the world with whisky - but it has got a long way to go to catch up with Scotch," he said.
"So I wanted to invest in that, I wanted to be part of that.
"I didn't want to try doing it back home or some other market, I wanted to do it here."
He said it was "very exciting" to have Bladnoch in his "stable of businesses".
"I suppose our vision is to see this as a very, very vibrant and big, functioning distillery creating a lot of employment for this region and to be the cornerstone of this community," he said.
"That is what we are working towards."
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Transport group Stagecoach has placed orders for about 480 buses and coaches in deals worth a total of £97m.
[NEXT_CONCEPT]
A man, who downloaded thousands of images of children being sexually abused, has been released on probation.
[NEXT_CONCEPT]
The new owner of Scotland's most southerly distillery has revealed ambitious plans for its future.