The majority of buses in a County Durham town will now be run by one firm after the Office of Fair Trading (OFT) cleared the sale of several routes.
Arriva North East will take over Stagecoach's Darlington operations following the go-ahead from the consumer affairs watchdog.
Stagecoach's town operations and its 78 staff will transfer to Arriva as of Sunday.
Workers will see no change to their pay and conditions, Arriva said.
The firm also intends to move from its current town centre base at Feethams to Stagecoach's more modern depot in Faverdale.
Liz Esnouf, commercial director for Arriva North East, said: "We are very pleased with the Office of Fair Trading's decision to clear the deal.
"On behalf of Arriva I would like to take the opportunity to welcome Stagecoach's Darlington staff to Arriva North East.
"From 26 August all daily, weekly and monthly town area tickets will be valid on all Arriva and/or former Stagecoach services in the town area. Arriva borough area tickets will also be valid on former Stagecoach town services."