The scheme, funded by Northumberland County Council, includes the refurbishment and re-modelling of the centre to provide modern leisure, library and community spaces.
As a result, the centre will be closed to the public while the internal layout is changed.
Alternative arrangements have been introduced for customers and sports clubs, starting on November 1.
Once the work is complete, the centre will provide a new and improved sporting offer.
The ground floor gym area will be refurbished and reconfigured to provide a dedicated cycling/spinning studio while the first floor will be converted into a new gym area with weights and state-of-the-art cardio equipment.
In addition, the three squash courts and viewing gallery will be refurbished and the six-court sports hall upgraded.
There will be new and improved changing facilities available for sport and community use, including changing places that are designed to be fully accessible for those with additional needs.
A new, modern and welcoming reception area, a library and the creation of a community café and hub area are also included in the scheme as well as essential repairs to the fabric of the building.
The County Council has also been working with Newbiggin AFC, local clubs and the Football Foundation to provide new and enhanced grass pitches to the rear of the centre.
The work is expected to take nine months, with the centre scheduled to re-open in summer 2022.
Cllr Jeff Watson, cabinet member with responsibility for health lives, said: “This upgrade work will breathe new life into the centre and provide a modern and much improved experience for the local community.
“The start of the work on site marks another milestone and means we are one step closer to bringing these fantastic new facilities to the local community.”
Mark Warnes, Chief Executive of Active Northumberland, said: "We want to thank our members for their patience and understanding as we undertake this exciting project.
"We look forward to welcoming them to Ashington Leisure Centre through this period of transformation that will see a dramatic improvement in the quality of facilities at Newbiggin Sports & Community Centre for our Active Northumberland members and customers."