ICON Ipswich is on track for a September completion as construction of the ninth floor of the Bell St building is finished.
The $93 million tower will welcome 1200 public servants on October 1, the first day the Queensland Government's 15-year lease.
The "topping out" milestone was achieved on schedule, Leighton Properties project director Bradley Norris said.
"To see the exterior of the building taking shape is an exciting stage in the development's progress, and is a clear demonstration of the continued progress of Ipswich," he said.
"We are also on track to achieve practical completion by September 2013."
The 117 Brisbane St address covers 15,000sq m of commercial space together with 750sq m of ground floor retail.
Leighton Properties is continuing to progress negotiations with several national retailers for the ground floor retail tenancies.
Mayor Paul Pisasale said he remembered when the iconic Cribb and Foote store occupied the site.
Now the address is embarking on a new iconic future.
"This is only the start of the journey. We are talking about a very historic site that was the heart and soul of Ipswich," he said.
"The Icon Ipswich building will now become another icon. The hardest thing is to get the rest of the CBD going. The partnership between the CBD and Riverlink will become more important.
"This iconic landmark is supporting local jobs - it will boost our local economy and drive further commercial interest in Ipswich - helping to grow our city and the surrounding region."
Work began on Icon Ipswich in late 2011 as the CBD took its first steps towards a major overhaul.
Doubts whether the State Government could attract public servants to voluntarily work in Ipswich were raised when Premier Campbell Newman admitted public servants did not want to move.
But Cr Pisasale plans to hold an open day in a bid to convince public servants Ipswich is a great place to live and work.
The second Icon Ipswich tower is expected to have eight levels.
It will be home to 1200 public servants.