The initial seven-year contract starts in from April with a provision to extend to 15 years.
The deal will save East Thames around £4m a year on planned and responsive repairs and maintenance to its 13,500 households.
East Thames director of development and property, Geoff Pearce, said: “We are very much looking forward to working with our new partners Interserve and welcome their customer centred approach to delivering our repairs service.
“Thanks to the feedback we’ve received from our residents, we have been able to work, together with Interserve, to design a service that better meets the needs of our customers, while delivering value for money and a significant contribution to East Thames’ local employment aims.”
Bruce Melizan, executive director at Interserve, said: “Delivering front-line services for East Thames is strategically important to us at Interserve, as it affects local residents’ homes and their quality of life.
“The fact that East Thames has given us an opportunity to share our knowledge and experience in delivering residential repairs and maintenance with them is a strong endorsement of the value and quality we can bring to their estates.
“The benefits of our approach have already been evidenced by the 22 per cent saving we have already achieved for East Thames on their outsourcing model, which is just the start of a partnership that will enable East Thames and their residents to benefit from our intelligent approach to delivering services over the coming years.”