Work getting underway at the complex in Jarrow includes an extension of the gym space with the addition of a mezzanine floor, a new sauna and the refurbishment of the changing rooms, and an outbuilding to be used in supporting athletics events.
Leisure chiefs say the scheme is expected to take around six months to complete and will require the closure of the gym, sports hall and changing rooms for the duration of the works.
While a number of fitness classes will continue to be provided on site, they said, a selection has been temporarily relocated to Jarrow Focus and Hebburn Central in order to accommodate the improvements.
All other areas will remain open as usual.
Last admissions to the gym are today, Friday 17 June, while the sports hall and changing rooms will close from Monday 20 June.
The stadium, in Dene Terrace, is a major athletic venue for the borough, which plays host to regional and national events and is home to various sports clubs including Jarrow and Hebburn Athletic Club.
It has also acted for a training facility for teams participating in international events over the years.
Council chiefs say the internal revamp of Monkton Stadium is the latest in a series of investments in leisure and library facilities.
It follows the new state-of-the-art facilities at Jarrow Focus, Hebburn Central, The Word, Haven Point and Jarrow Pool.
Councillor Joan Atkinson, Deputy Leader of South Tyneside Council with responsibility for Culture, Leisure and the Visitor Economy, said: “We are committed to helping to improve the physical health and wellbeing of our residents and our sports and leisure centres continue to play a central role in this.
“Over the last ten years we have heavily invested in our leisure facilities. We’re delighted to be able to build on this further and now make improvements to Monkton Stadium, which is a much-loved community sports facility in South Tyneside.
“The upgrade will bring it into line with our other centres and help us to provide the very best leisure facilities for our residents and visitors.”