The tragic accident occurred in Langton View in East Calder, Livingston, shortly after 11.30am on Saturday.
A 67-year-old man was rushed to the Edinburgh Royal Infirmary where he later died from his injuries.
It is understood that the man’s son was also present when the wall collapsed. However, he escaped injury. Another man, named locally as Ian Way, and who lives two doors away, was also rushed to the infirmary where he was found to have suffered three fractured ribs, a broken sternum and a punctured lung.
A fourth man is understood to have lost the fingertips on one hand and sustained minor leg injuries.
The men had been attempting to knock down the wall of a garage at the side of the property when it buckled and fell on them.
Ralph Walker, 54, told how his wife was “devastated” after witnessing the accident from across the street.
He said: “My wife had looked out the upstairs window to check the weather as we were about to go out and she saw the three guys trying to knock down the garage wall. They had already taken the roof off it and began pushing it back in towards the house to collapse it.
“The wall kind of bounced back towards them and when they pushed it again it buckled out the way on top of them rather than in the way they had expected.
“The old guy took the brunt of it as he was in the middle.
“All the neighbours ran over to see what had happened. When I got there the guy had been pulled clear but he didn’t look too good. His son was in a terrible state. It’s a real tragedy.”
Another neighbour, George Clarkson, 65, lives opposite the house and he told how the men were removing the garage ahead of an extension at the property of Alex and Sharon McDowell.
He said: “I heard the bang around 11.30am and ran out. I couldn’t believe what I saw.
“I think three of the guys were builders.
Big Ian from across the street was just lending a hand as he’s a good friend of Alex. His two kids went running to find out what had happened so I grabbed them and held them back.
“The emergency services gave the guy CPR at the scene but he didn’t respond.”
A spokesman for Lothian and Borders Police said: “Police and the Health and Safety Executive are now conducting a joint investigation to determine the full circumstances surrounding this incident.”
The name of the dead man has not been released.