The High Court ruled that the consultation process for compensating those affected by the HS2 high-speed rail scheme "was so unfair as to be unlawful".
The decision was a victory for the High Speed 2 Action Alliance (HS2AA), which consists of more than 70 affiliated action groups and residents' associations.
The HS2AA case was one of five separate cases brought to block the rail scheme in its current form - it was the only case to succeed.
Mr Justice Ouseley, sitting at London's High Court, is now hearing submissions from lawyers on the appropriate remedy.
Joe Rukin from Stop HS2 told ITV News Central that he remains optimistic about the outcome of today's review.
The High Court is expected to give its ruling on a number of legal challenges to the government's plans for HS2 later today.
Opponents of the high speed rail plans are asking a judge in London to declare the multi-billion pound project legally flawed and to reconsider the plans.
The first phase of HS2 would see a high-speed railway line running from London to Birmingham.
If successful, the legal challenge could potentially delay the scheme for years.
Judgment is being handed down by Mr Justice Ouseley at London's High Court. Whatever the judge decides, appeals against his decisions are almost certain to be taken to the Court of Appeal.
Key accusations include that the Government has unlawfully failed to undertake a strategic environmental assessment of the entire project before giving the go-ahead, or to arrange a consultation process "that allows informed responses on the true merits and demerits of the proposals".
There is also a dispute over the compensation arrangements being put in place for homeowners living near the HS2 line.
Some 172,000 properties within 1km of the first phase are reported to be affected by "a generalised blight" since the proposals were announced.
– Fazle Elahi, shopkeeper
The ambulance came really quickly. It looked like the William Hill sign had hit him. A woman at the scene was crying. He wasn't moving.
Health and safety investigators entered a flat above the shop to take photographs of the sign, which was made of metal and measured approximately 30ft.
A bunch of flowers had been left at the scene by a member of the public.
Ken Osbourne, who works at the nearby Woody Grill restaurant "Hundreds of people walk past here every day. It could've been me or any one of them. The shop has been there for about 10 years."
Ioana Nita, was working at a nearby restaurant and said; "I don't know how that can happen. The sign is huge. Everyone said he was just walking past the shop.
"I cross that way five times a day. That could have been me."
The sign, which had covered the length of the shop front, fell on to the pavement on a main road in Camden, north London.
Police erected a forensic tent on the pavement to cover the place where the man was killed, and cordoned off the surrounding area.
Ioana Nita, 21, was working at a nearby restaurant when the accident happened.
"I'm shocked. We heard a very loud noise. Me and a colleague went outside and saw the guy lying on the floor," she said.
"Five guys picked up the sign and it was put on the side. His hands were covered in blood and he wasn't moving.
"Lots of people were in a circle around him, then the ambulance arrived and they were trying to get him back to life, pressing on his heart."
Ken Osbourne, 28, who works at the nearby Woody Grill restaurant, said: "I saw the guy lying down in the road, covered in blood.
"The main impact was clearly on his head. I saw them trying to resuscitate him in the back of the ambulance."