One of Scotland's most historically significant buildings will be given a new lease of life after two decades of ownership disputes were resolved.

The semi-derelict Egyptian Halls, designed by Alexander "Greek" Thomson in the mid-1800s and dominating Glasgow's Union Street, will undergo a £5m clean-up and refurbishment before being marketed as a retail or office development.

One suggestion is it could return to its original use as a commercial outlet and be turned into an upmarket shopping centre, along the lines of the Princes Square mall on nearby Buchanan Street.

Various attempts to bring the halls, regarded as Thomson's commercial masterpiece and architecture of world-class significance, back into use have been hampered by what the owners describe as "18 years of intense, fractious and complicated wrangling".

Even plans to restore the building when Glasgow was City of Architecture and Design in 1999 failed because of ownership disputes. It currently lies vacant and covered in grime above shops.

A report from 2003 found the A-listed structure required a new roof and guttering; its cupola reinstated and extensive masonry repairs, while dry rot needed treatment and the windows and doors overhauled before the plasterwork could be reinstated.

The building's long-overdue return will begin when the project goes to tender in November, with developers moving on-site next May or June. The provisional completion date is December 2010 but this will depend largely on the outcome of discussions with Glasgow City Council and Historic Scotland as well as the planning process.

The deal to conclude ownership was sealed last week, with Dundee-based Union Street Properties buying the remaining 50% of the upper floors. Director Derek Souter said: "We have invested approaching £4m over the last decade to achieve 100% ownership despite numerous and complex obstacles.

"This will begin the process of re-energising Union Street, which is still one of Glasgow's busiest thoroughfares, whilst acting as a catalyst for more investment in the area - an objective which many stakeholders, including the council, have recently stated they would like to see achieved."

He added the final investment figure, thought to be around £5m, and the eventual purpose of the halls would be determined by trading conditions when it is marketed.

A Glasgow City Council spokeswoman said: "We look forward to working with the new owners to bring forward the scheme of repairs which will return this very important building to its original condition."