The free party on Saturday 21 June has a host of fun and games for all the family, from parkour to face-painting and street art to scientists on stilts.
And at 12 noon, the new Mayor of Rugby, Cllr Barbara Brown, unveils the latest addition to Rugby's iconic collection of contemporary British art.
While the identity of the artist behind the new acquisition remains under wraps until the birthday bash, it can be revealed the artist has been nominated for the Turner Prize, received an MBE for services to British art and was recently elected to the Royal Academy of Arts.
Before the bash begins, a 'creative creatures' children's parade takes place in the town centre, starting from St Andrew's Church at 10.30am before making its way to the art gallery and museum.
Children and families from schools and community organisations have worked with artist Kate Morris to create costumes and crafty creatures for the parade.
The birthday bash starts at the Little Elborow Street venue at 11am, with Ascension Dance delivering pop-up parkour workshops for youngsters who want to experience the freedom and flow of freerunning.
Four, half hour-long parkour workshops take place during the day, with places bookable in advance, together with drop-in sessions starting at 11.45am and 2.30pm.
The Irregular Art Hub hosts a street art workshop throughout the Big Birthday Bash, perfect for a budding Banksy to experiment with stencils and spray paint, while Far Out Faces offer free, animal-themed face-painting inspired by the forthcoming Great and Small Crafted Creatures exhibition, which opens on the day of the bash.
Science on Stilts tour the venue during the party, with professional scientists - and accomplished stilt walkers - entertaining with simple experiments and answering visitors' scientific questions, and event illustrator Esther Sketches captures the creative spirit of Rugby Art Gallery and Museum with live illustrations inspired by the venue and visitors.
Visitors can enter the birthday spirit by creating a pom-pom party hat and helping to decorate a giant cardboard birthday cake, while Do Touch bring a sculptural world of squishy, monster creatures perfect for children under six to get to grips with and explore.
And the council's Play Rangers team promises to bring Absolute Playhem to the Big Birthday Bash with a range of fun activities for children.
Artist Mark Curtis Hughes reveals the secrets of papercut art during a mask-making workshop until 12 noon, when he hosts a special preview of his Ocean of Noise exhibition, which runs at the venue's Floor One Gallery from the 17 to 28 June.
Director's Cut bring a photobooth to the bash so visitors can take home a free birthday snap, and visitors can take home a unique memento from the birthday bash courtesy of Hello Sunshine illustrator Jo, who creates fun, ten-minute live portraits - either single or a whole family.
Cllr Maggie O'Rourke, Rugby Borough Council portfolio holder for partnerships and wellbeing, said: "The Big Birthday Bash encapsulates everything Rugby Art Gallery and Museum has stood for during the past 25 years - encouraging visitors to learn, enjoy, create and discover.
"The birthday bash provides opportunities aplenty to get involved and have fun, so come along, join the celebrations and have a great day out exploring everything Rugby Art Gallery and Museum has to offer."
Cllr Neil Sandison, Rugby Borough Council's Liberal Democrat spokesperson for partnerships and wellbeing, said: "The Big Birthday Bash promises to provide great fun for all the family, the young and the not-so-young, and you will have a great time with lots to see and do throughout the celebrations."
For more information about the Big Birthday Bash - and to pre-book places at the parkour workshops - visit www.ragm.co.uk/birthday-bash