Police were called to Sipson Lane, Harlington at 6 p.m. 06:16 Sunday, October 31, after a passing motorist noticed a person next to the road.
Officers attended along with London Ambulance Service paramedics. They found a man believed to be in cardiac arrest.
Despite the efforts of the emergency services, he was declared dead on the spot at 07.00.
His death is being treated as suspicious and a murder investigation has been launched.
An autopsy will take place well in advance.
Although formal identification has not yet taken place, officers are convinced the deceased is 28-year-old Mohamed Muhiyidin from Southall, Ealing.
His next of kin have been informed and are being supported by specialists.
Detective Melanie Pressley of Met’s Specialist Crime Command said: “We do not yet know how Mohamed got to lie wounded at the roadside this morning, but there will be people out there who know.
“I would appeal to anyone with information about this incident to sign up. I would also like to ask anyone who knew Mohamed and perhaps knows why anyone wants to harm him to speak to us.
“In addition, I would appeal to anyone driving along Sipson Lane on Saturday or in the early hours of Sunday morning to check any dash cam footage they may have to see if they caught anything unusual.
“A family is grieving after hearing the terrible news that their loved one has been murdered. We will do everything we can to find out who is responsible, but we need the help of the public.”
Anyone with information should call 101 with the reference 2365 / 31OCT.
Information can also be given to Crimestoppers, anonymously, by calling 0800 555 111 or by visiting www.crimestoppers-uk.org