A large turnout is expected for the service for Stephen Heaney in his home town of Limavady.
The 50-year-old collapsed around five miles into Monday’s race.
Mr Heaney took ill near the Sydenham bypass and passed away in the Royal Victoria Hospital a short time later.
His funeral will take place at Christ Church in his home town of Limavady at 2 pm today, followed by interment in the adjoining churchyard.
Mr Heaney, who was a serving police officer in the town, was honoured in 2009 when he was presented with a Royal Humane Society bravery award for rescuing a man from a burning building.
Mr Heaney was a father of two girls, Rebecca and Victoria, who are being comforted as they struggle to come to terms with their loss.
On her Facebook page, Victoria paid tribute to her father, writing: “I hoped that today [Tuesday] I would have been congratulating you on completing your first marathon.
“God had other plans and decided to take away the best man of my life, a role model through being a dad, a supporter, a sports player and a gentleman to everyone he crossed.
“Rest easy daddy, I love you so much and I’m so proud of you.”