Work will start this month and be completed by August 2013 on The Forum building.
Wates saw off competition from big name rivals including Kier, Willmott Dixon, Volker Fitzpatrick, Vinci and Bam.
Wates will now source up to 75% of its supply chain from within a 50-mile radius of Southend.
The Forum scheme is a joint enterprise between Southend-on-Sea Borough Council, the University of Essex and South Essex College of Further & Higher Education.
Derek Jarvis, Executive Councillor for Culture & Tourism, said: “I am delighted that we have now appointed a contractor and that work on The Forum can begin in earnest.
“A huge amount of ground work has been done just to get us to where we are today, but the appointment of Wates as main contractors brings everything into sharp focus.
“Once they take possession and people start seeing their machinery moving around the site it will all start to become very real. It‟s very exciting.”
Ian Vickers, Managing Director for Wates Construction, said: “We will deliver an exceptional building, but more importantly we will immerse ourselves in the local community.
“We have committed to using local labour where possible, and want the project to be used as an educational tool in Southend-on-Sea.
“We will be providing many work experience placements, taking on a number of apprentices, running community days, and putting local unemployed people through our Building Futures programme, which gives further opportunities of employment or training. This is a very exciting time for the local community, and we are proud to be part of it.”