Wynne was awarded the £4.2m main construction contract in March.
Following the completion of the marine works within the harbour, the construction phase of the project will provide a centre in Pwllheli for national and international sailing events.
The facility, designed by Ellis Williams Architects, is scheduled to be open by Easter 2015.
Managing director Chris Wynne said: "As an established firm in North Wales, we are delighted to have been awarded this prestigious contract. Our proven experience in this field equips us to deliver the project to a high standard, providing Gwynedd Council and the community of Pwllheli with first-class facilities for sailing and outdoor activities.
“The project will also enable us to offer employment to a number of skilled workers in the area, as well as affording valuable opportunities for the future. The project has been widely welcomed by the local community and we are looking forward to starting."