The council sold the property, in Ingram Street, to Glasgow developer SCOT Sheridan for more than £4 million.
It was declared surplus to requirements by the council as a result of its Tomorrow's Office scheme.
That has resulted in the number of its city offices being cut from 19 to six, saving the local authority £5.9m a year for the next 25 years – a total of almost £150m.
SCOT Sheridan is planning to strip the six storey listed building back to the brickwork and create a 132-bedroom, four star hotel.
Director David MacLachlan said: "We are speaking to three or four different operators but no decision has been made yet as to what brand will run it.
"Work will start this time next year and is due for completion in spring 2015."
Around 100 jobs will be created as a result of the construction work and staffing the hotel.
Mr MacLachlan added: "There are not many buildings of this size that are capable of being converted.
"The Merchant City is key for every hotel operator."
However, the company boss could not put a figure on how much the conversion work would cost.
According to Glasgow City Marketing Bureau, there is a need for an extra 17,000 hotel, guest house and bed-and- breakfast bedrooms in the city and surrounding area.Chief executive Scott Taylor puts that down to a continuing increase in the number of conference delegates and visitors coming to the city all year round.
He said: "Occupancy averages for this year are looking positive and the hotel trade in December and January has reported above last year's takings.
"We are looking forward to a positive tourism year in 2013 while 2014 and 2015 will be stellar.
"We have three months of this financial year to go and conference sales figures are already up 25% on last year.
"Conference sales through Glasgow City Marketing Bureau are £152m in this current financial year – last year they were £120m."
Mr Taylor said of the planned new Merchant City hotel: "There is no reason to think another city centre boutique hotel will not do well."