The 61-year-old was attacked and beaten by LVF members as he locked the gates at Bellaghy Wolfe Tones GAC on May 12 1997.
The Bellaghy club chairman was then put in the boot of his own car and taken to a country lane outside Randalstown in Co Antrim where he was shot six times.
His remains were later found beside his burning car.
No-one has ever been charged in connection with his murder.
One of those involved in his murder was an MI5 agent from Belfast who now lives in England.
The brutal killing of Mr Brown stunned the GAA community across his native county and further afield.
Mr Brown’s family were dealt a second blow last October when his son Damian, who was prominent in his family’s campaign for justice, died after a short illness.
His son Damon said the Brown family continues to wait on an inquest to be held.
“It’s a bitter pill that we are still waiting, 25 years on, for an inquest,” he said.
“The burden this has put on the family is inexcusable.
“What is it they are so afraid will come out about the murdered of my granda?”
Paul O’Connor, of the Pat Finucane Centre (PFC), said state agencies must take responsibility for continuing delays.
“The family of Sean Brown have shown tremendous dignity and patience,” he said.
“But the fact that Damian had to spend years traipsing up and down to Belfast for preliminary hearings is a disgrace.
“Both the PSNI and the MoD must share responsibility for these appalling delays.
“On this poignant anniversary our thoughts are with Sean and Damian and the Brown family.”
Mr McCarthy is expected to plant a tree in memory of the murdered GAA official and a plaque will be unveiled at the Seamus Heaney inspired ‘Turf Man’ statue in Bellaghy at 6pm.
A piece of work by Seamus Heaney, who knew and wrote about Mr Brown, will also be read by Belfast actor Stephen Rea while Mass will be held in the grounds of the nearby Bellaghy GAA club at 7pm.
Several events have also been organised to take place this weekend, including an update in the case presented by the Pat Finucane Centre and Niall Murphy, of KRW Law, on Saturday at 6.45pm.
The acclaimed ‘In Their Footsteps’ exhibition will also be on display from today.
Meanwhile, it is understood there may be an important development in a High Court civil case taken by Mr Brown’s widow at a hearing due to be held today.Tags: