Mayor Richard Parker announced that the WMCA board has given the green light to the acquisition from National Express parent company Mobico Group.
The mayor said the move is part of his push towards franchising.
Mobico Group, the parent company of National Express West Midlands, also confirmed it was reducing its operational risk and had reached an agreement in principle.
National Express is the biggest bus operator in the region, accounting for around 94 per cent of bus journeys in the West Midlands.
Its regional operation includes around 4,800 staff, 1,300 buses and nine depots.
Buses account for around 80 per cent of all public transport journeys in the West Midlands, carrying around 4.6 million trips each week.
WMCA has now approved a managed acquisition to protect passengers, staff, services, depots, fleet and the wider bus network.
The mayor said: “I wasn’t prepared to stand by and watch hundreds of buses disappear from our roads because a private company decided to walk away.
“People rely on these buses to get to work, to school or to hospital appointments. They are a public service and I believe they should be run in the public interest.
“So we stepped in. We protected the services people depend on, protected jobs and kept the West Midlands moving.
“For too long, decisions about our buses have been driven by what works commercially, rather than what passengers and communities need. That is what has to change, and I am changing it.
“I won’t shy away from taking difficult decisions in the public interest. We are continuing to push ahead with franchising because I want decisions about routes, fares and timetables made here in the West Midlands, with passengers put first.
“There should be no doubt who our bus network ultimately answers to - the millions of people who rely on it every single day.”
