The 81 bus service is currently run by National Express West Midlands.
But from Sunday, daytime journeys from Monday to Saturday will be run by Wolverhampton firm Banga Buses, who say the route is no longer commercially viable for their rival operator.
Banga Buses said in a statement: "The service 81 was no longer commercially viable for National Express to operate, so we together with Transport for West Midlands managed to incorporate the service into one of our tenders. This will replace the service 52 which is withdrawn due to poor usage.
"We are pleased to operate the service 81 from Monday."
National Express West Midlands will continue to operate the route after 6pm from Monday to Saturday, plus all day on Sundays.
Customers who have a National Express-only ticket or pass will not be able to use it on Banga Buses.
They can call National Express on 0121 254 7272 to upgrade their ticket - this can be done over the phone.
In addition, from January 30 the route will be slightly different where it goes through Blakenhall.
Buses will now operate via Silver Birch Road and Pond Lane instead of Derry Street.