Developer Doug Gray said the first stage of the project would become a reality this year, about 18 months after the concept came to life.
"It's what we've been waiting for. It's a wonderful outcome after a long process," Mr Gray said.
"Providing we get all the paperwork signed, we will start building on Monday."
The first stage of the project will cost $8 million and will involve the redevelopment of the Origin Energy cottages in Boland St into private office space, a walking boulevard, a cafe with outdoor garden, a new 4000sqm Government service centre for Centrelink and car parking.
It should take about 10 months to complete.
Stage two of the Cimitiere St development includes retail outlets, restaurants, residential apartments and offices, the continuation of a boulevard to link the river with the City Park and historic interpretation features in the horizontal retort building.
The development was dependent on the RPDC ratifying the Launceston City Council's decision to rezone the site from particular use to a new business zone.
The business zone - established by the council's amendment 139 to facilitate the development of bulky goods on the city fringe - has been partially approved by the RPDC.
A meeting will be held tomorrow between the council and RPDC staff to clarify a number of points before the amendment is officially approved.
While the issues of contention do not impact on the Gasworks, it is understood they are critical to the future of the $30 million Bathurst St car park redevelopment.
Meanwhile, the council yesterday refused a planning permit for a $2 million third stage of the gasworks development.
Mr Gray had applied for a rezoning of the Origin Energy car park - a section of land on the north- west corner of the Willis St car park - to allow for the development of six multiple dwellings, two shops and peripheral sales.
Aldermen took the advice of planning staff who said the development would create spot zoning and could be ad-hoc.
They said the site was an integral part of the city block and should be developed in a complementary way to the Willis St site - which had previously been the subject of an approval recommendation for a Woolworths supermarket.
It is not known what action the developers will now take.
Gasworks development and site rezoning approved by RPDC yesterday.
Amendment 139 - a new business zone for the city - will be officially ratified by the RPDC on Wednesday. It will include guidelines for big-box developments by stipulating the allowable number and size of shops and what can be sold in them.