The renovation will cost a total of $574,000 and is due to begin in late 2019.
BayTrust's grant is the first major step towards raising the funds required and St Chads is in early discussions with other community funders.
Mayne said they felt very privileged.
"This is a big chunk of the funding we need to get started and we really appreciate BayTrust's ongoing support. We want to face the future knowing that we're becoming more sustainable and less reliant on philanthropic grants long term.
"We want to maximise the assets we have, like our building, so we can become more financially sustainable."
A renovated hub will be more appropriate for the needs of St Chads' clients and will also help support future social enterprise initiatives.
"We also want the community to be able to visit our gallery and join us for classes and events alongside people with disabilities. We want this building to become a community facility everyone can enjoy."
A total of 43 possible projects were considered by BayTrust after applications were called for earlier this year. These were narrowed down to four which best fitted with BayTrust's "outcome areas" and overall vision of ensuring the Bay of Plenty is the greatest place to be.
BayTrust chief executive Alastair Rhodes said trustees wanted to help St Chads become a strong and sustainable organisation so it can continue its work for many years to come.
"The community connections they build and the life skills they teach their clients are invaluable. Having a building that's warm, safe, accessible and fit for purpose is a crucial way in which we can support them and their future aspirations."
Rhodes said the Community Amenities Fund was designed to grant between $100,000 - $500,000 to capital projects that deliver new permanent facilities, or upgrade and preserve existing community and environmental assets.
"We have set aside $1.25m annually for the new Community Amenities Fund and are looking to support intergenerational community and environmental assets that make a real difference in people's lives."