The British distance great, a four-time Olympic champion on the track, announced in January that 2023 would be his final year as a top-flight athlete.
Farah missed last year's edition with a hip injury but the 40-year-old, who has been in training in Ethiopia, is now ready for one final appearance.
"Sunday will probably be my last marathon in terms of just being realistic," Farah told a press conference in London on Thursday.
"It will be my last marathon. It won't be my last race but in terms of the marathon, the London Marathon will be my last."
He added: "I started the mini-marathon here so for me it will be quite emotional. I remember (when I was) 14 years old, I was here watching great athletes running on the Sunday and I was here taking part in the mini-marathon.
"The support, the people coming out in London, I think that will get to me but I will try not to think about it and run. After the race maybe there might be a bit of tears and emotion."
Farah won gold in both the Olympic 5,000 and 10,000 metres at the 2012 Games in London before retaining both titles in Rio four years later.
But he failed to qualify for the Covid-delayed Tokyo Olympics, which took place in 2021, and has struggled with injuries.
"As an athlete, you always want to go out there and do the best you can but the last two years my body hasn't allowed me to do what I needed to do in training," said Farah. "That's been the hardest thing."
