The pedestrian believed to be in his 50s suffered head and leg injuries, following the collision on Wednesday (September 27) morning.
He was taken by paramedics from the London Ambulance Service (LAS) "as a priority" to a west London hospital.
Emergency services were called to the scene at around 11.20am.
A Metropolitan Police spokesman said: "Police were called by the London Ambulance Service at around 11.22am on Wednesday, 27 September to reports of a collision between a car and a pedestrian in Lampton Road, Hounslow.
"The pedestrian, a man believed to be in his 50's, was taken to a West London hospital with head and leg injuries.
"We await an update on his condition."
A LAS spokesman said: “We were called today at 11.20am to Lampton Road, Hounslow to reports of a road traffic collision.
“We sent an ambulance crew and a single responder in a car to the scene.
“We treated a man for a head injury at the scene and took him to hospital as a priority.”
Lampton Road was closed in both directions between A4 Great West Road and Alexandra Road.
Cars and buses were placed on diversion while emergency services dealt with the incident.
No arrests have been made and police enquiries continue into the accident.
Keep up to date with the incident in our live blog.
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