The money, raised by National Lottery Players, will safeguard for future generations the iconic Greek-classical portico, pillars and steps that grace the church in New Road.
The frontage is a popular Brighton landmark sited amid other celebrated neighbours at the heart of Brighton's cultural quarter, such as the Corn Exchange, Theatre Royal and Royal Pavilion.
The Grade II listed building was the work of famed Brighton architect, Amon Henry Wilds.
Countless city-dwellers and visitors know the building as a liberal and open-minded church, a popular host of weddings, child-namings and memorial services, and also as a thriving concert venue.
But an expert survey in 2016 discovered that rainwater had begun to penetrate the stucco frontage, threatening the cream-coloured Doric columns and portico with structural collapse.
So perilous was this internal damage that Historic England - the public body that oversees the nation's finest old buildings, placed the church on its Heritage at Risk Register.
Fortunately for the city's heritage, Brighton Unitarian Church is home to a thriving spiritual community that refused to allow its beloved architectural jewel to fall into disrepair.
Church members launched a vigorous fundraising campaign which has included a busy programme of lunchtime concerts, organ recitals, quizzes and fairs.
They also turned to the Heritage Lottery Fund (HLF) for crucially needed help. Volunteers compiled a detailed dossier of the repairs required, along with a programme of planned works and fundraising to achieve it.
Now, to the campaigners' joy, the HLF has agreed to fund 53 per cent of the project costs, with a grant totalling £227,500.
This will fund the repair and restoration of the classical portico, as well as an activity programme to raise awareness of the building"s remarkable history.
Jef Jones, the congregation's lay leader, says: "We're pleased and excited that the Heritage Lottery Fund are giving us a grant to help restore our church.
"It has been at the heart of liberal religion in Brighton for nearly two hundred years and it"s a great community resource and concert venue.
"We can look forward now to getting on with the work and conserving the church for future generations."