Police were called at approximately 7.15pm on Sunday, 13 December to reports of a stabbing in St Anns Road, Harrow.
Officers and London Ambulance Service attended.
A man – believed aged in his 20s – was found suffering stab injuries; despite the efforts of the emergency services, he was pronounced dead at the scene.
Two further males – both believed aged in their late teens – also suffered stab injuries. They are both at hospital receiving treatment; condition awaits.
Crime scenes remain in place in and around the St Anns Road and Station Road area.
Enquiries into the circumstances continue.
Anyone with information that could assist police at this early stage is asked to call 101 and quote CAD6149/13Dec.