Ritchies director Andrew Ritchie said DesignLine, in Rolleston, near Christchurch, was chosen ahead of Chinese and Japanese suppliers and the mix of 40 and 48-seat buses would have the latest in emission controls.
The first delivery is scheduled for March.
"Another reason we signed with DesignLine is because they have the capacity to handle such a big order, and if we need to accelerate the programme at any stage, we are able to do this," Mr Ritchie said.
Ritchies, which includes brands Intercity and Newmans, was started in Temuka in South Canterbury in 1937, with three buses.
It is now the largest privately-owned bus company in New Zealand and Australia, with a fleet of 900 operating from 14 depots.
Last year, DesignLine produced 200 buses and expects to complete 250 this year.
Investment for the Ritchies order would boost capacity to 500 buses a year.
