Foundations had been installed in January, before the first Vestas V112-3.45MW turbine was put in place in early March.
Further cabling work, and more construction and commissioning work will continue on both the offshore and onshore substations, joint owners E.on said.
First generation of electricity from the Rampion site is expected by the end of the year, and the project is due to go online in 2018.
Chris Tomlinson, development and stakeholder manager for the project, said: "We’re especially proud to have achieved this remarkable feat, installing all 116 turbines ahead of schedule in just over six months.
Each turbine consists of an 80-metre tower, weighing approximately 200 tonnes, and three 55-metre blades.
Two jack-up vessels, the MPI Discovery and MPI Adventure, transported components for eight turbines at a time from Esbjerg in Denmark to the site, which is owned by E.on, the Green Investment Group (formerly Green Investment Bank) and Canadian energy company Enbridge.