The Perth-based group has unveiled orders for 568 vehicles in 2014/15.
The firm, which describes itself as Britain's biggest bus and coach operator, said the set of orders is its largest ever and one which will support hundreds of British jobs.
The move takes Stagecoach Group's total orders of new buses and coaches for its regional UK operations to around £545 million in the last seven years, bosses said. The group has also ordered more than £100 million of new vehicles for its London bus operations since buying the business in 2010.
Of the overall investment in the next financial year, £81 million is being spent on 495 new vehicles to go into service across Scotland, England and Wales.
In addition, a £21 million fleet of more than 70 greener hybrid buses will be introduced to the London operation.
All of the new vehicles will be fitted with CCTV while more than 350 will have wi-fi installed for free internet access.
The latest orders follow an annual competitive tendering process, and the first of the new vehicles will be delivered from spring this year, the firm said.
Stagecoach said the "vast majority" of the new buses and coaches will be produced in the UK, supporting British manufacturing jobs and small businesses.
Group chief executive Martin Griffiths said: "This record investment is a major boost for UK jobs in manufacturing and many other smaller businesses in the supply chain.
"It is also a huge vote of confidence in the future of bus and coach travel in Britain. By investing in quality and continuing to offer the best value travel of any major operator in the UK, we can help people save money, rely less on their cars and use a greener way to access work, health, education and leisure."
At the end of last year, Stagecoach delivered robust performance in its bus and coach divisions, posting a 4.6% hike in half-year regional bus revenues.