“At 3:00 pm (1300 GMT) we will be at the top of the stairs to observe a minute of silence,” Cannes chief Thierry Fremaux said, adding that a fireworks display planned for the evening had been cancelled.
“I want to express our solidarity with the city of Manchester,” Fremaux said before a screening at the world's biggest film festival.
“We must show that we will not be bowed and that life will continue.”
Security has been tight for the past week in the southern French resort, where a host of A-list stars including Nicole Kidman and Will Smith have flown in for the festival.
Just 10 months after the jihadist truck attack in nearby Nice that killed 86 people, unprecedented measures have been taken to protect the Cannes festival, with large concrete barriers put up in a bid to prevent another vehicle assault and snipers positioned on the roof above sensitive sites.
Cannes Mayor David Lisnard also offered his “heartfelt thoughts” to families of the 22 killed and dozens injured in Monday night's attack at an Ariana Grande stadium concert in Manchester.
“The threat is at maximum. We will stay on maximum alert to prevent it and protect everyone, residents and festival-goers, from the risk of an attack,” Lisnard said on Twitter.