Newtown’s Oriel Davies Gallery confirmed the closure in a post on its website.
The Park-based gallery said it would be shutting in mid September, and will be closed until spring next year.
The closure is to allow for significant improvements to the building, being paid for with nearly £1m of Welsh Government investment through the Arts Council of Wales.
The work will improve the ‘infrastructure, security, environmental controls’ and the replacement of the roof at the gallery.
The improvements come as the galley becomes a partner in the National Contemporary Art Gallery for Wales, with the National Museum and the National Library.
A statement on the gallery’s website said: “Oriel Davies will be closed from mid-September until the spring 2025.
“This investment will enable us to bring works from the National Collections to Newtown to display alongside contemporary visual art.
“We will continue our work in the community during this time – check our website for upcoming events
“We would love you to come and show your support in our current Consultation Station in the gallery or please compete our survey online.
“On behalf of director Steffan Jones-Hughes and the team, we want to say a massive thank you to all the artists, makers, coffeemakers, coffee drinkers, dog walkers, art lovers, gift buyers, Newtown communities and businesses for supporting the gallery!
“We thank you also for your support and patience at this time for the gallery and we look forward to continuing to work with you to share and communicate this exciting news.”