Eden Hazard's penalty secured Chelsea the FA Cup for the eighth time as they beat Manchester United in what could be Antonio Conte's final match in charge.
Hazard sent goalkeeper David de Gea the wrong way at Wembley, having won the kick when brought down by Phil Jones.
United, having offered minimal attacking threat in the first half, were much better in the second.
Alexis Sanchez had a goal ruled out for straying just offside – referee Michael Oliver using VAR to confirm the call.
Thibaut Courtois later denied Marcus Rashford, before Paul Pogba headed wide with a clear chance from a corner.
Romelu Lukaku and Anthony Martial, who had both been doubts for the final because of injury, appeared as substitutes for the final 17 minutes, but United were unable to find an equaliser.