Managing director Ralph Robert said the company's number one priority is to reassure customers that "99 per cent" of bus routes won't be affected - and that starting and finishing times will remain the same.
His comments come amid concern from Barrhead's MSP, Hugh Henry, that services could be impaired by the company's takeover of the Arriva West business, which is set to be finalised by March.
He fears fares could rise and jobs be put at risk because McGill's - which will be the country's third biggest bus firm - will have a local monopoly.
And along with Paisley North and Renfrewshire MSP Jim Sheridan he's concerned the firm won't, as he sees it, negotiate properly with unions on any planned changes.
The situation facing workers is to be discussed at a meeting to be staged in the near future, but while union chiefs are able to attend it's unclear whether McGill's intends to consult or negotiate with them on any changes to jobs.
Meanwhile the firm's reputed £10million takeover of the Arriva business is being studied by the Office of Fair Trading, to determine if it's legal in competition terms.
But while the company awaits the result, Mr Robert says no time will be wasted in getting reliable information to customers.
He said: "McGill's remains confident of a positive outcome following our submission to the OFT.
"It is now imperative that the team here at McGill's turns its full attention to ensuring that we meet the information needs of our passengers."
"I can confirm that, based on the registrations currently being finalised for submission to the Office of the Traffic Commissioner, ninety-nine per cent of all routes will be retained by McGill's. I am also pleased to advise existing passengers of both McGill's and Arriva, that there will be no change to the start and finishing times across our services."