Robert Downey Jr. as Dr. John Dolittle

Harry Collett as Tommy Stubbins

Michael Sheen as Dr. Blair Müdfly

Jim Broadbent as Lord Thomas Badgley

Antonio Banderas as King Rassouli

Jessie Buckley as Queen Victoria

Emma Thompson as Poly (voice)

Rami Malek as Chee-Chee (voice)

John Cena as Yoshi (voice)

Kumail Nanjiani as Plimpton (voice)

Craig Robinson as Kevin (voice)

Ralph Fiennes as Barry (voice)

Tom Holland as Jip (voice)

Octavia Spencer as Dab-Dab (voice)

Selena Gomez as Betsy (voice)

Marion Cotillard as Tutu (voice)

Kasia Smutniak as Lily Dolittle

Carmel Laniado as Lady Rose

Frances de la Tour as Dragon (voice)

Jason Mantzoukas as James the Dragonfly (voice)

Ralph Ineson as Arnall Stubbins

Joanna Page as Bethan Stubbins

Sonny Ashbourne Serkis as Arnall Stubbins Jr.

Oliver Chris as Sir Gareth

Clive Francis as Archbishop

Paul Holowaty as Navy Man

Elliot Barnes-Worrell as Captain William Derrick

Mark Umbers as Lieutenant

David Sheinkopf as Don Carpenterino

Sid Sagar as Jeff the Prisoner

Martin Pemberton as Postman

Tim Treloar as Humphrey the Whale (voice)

Jim Carretta as Beard Mouse and Leona (voice)

Nick Fisher as Mini the Sugar Glider (voice)

Matt King as Clyde

Ranjani Brow as Mouse (voice)

Kelly Stables as Mouse (voice)

Scott Menville as Army Ant (voice)

Gia Davis as Baby Animal (voice)

Henry Holcomb as Baby Animal (voice)

Kyrie McAlpin as Baby Animal (voice)

Isley Zamora as Baby Animal (voice)

Stewart Scudamore as Pirate

Samson Kayo as Pirate

John-Luke Roberts as Pirate / Animal Performer

Joseph Balderrama as Prisoner

Daniel Hoffmann-Gill as Prisoner

Jane Leaney as Animal Performer

Josh Jefferies as On Set Chee-Chee / Animal Performer

Shaun McKee as On Set Yoshi / Animal Performer

Richard Soames as Animal Performer

Will Arnett as Rabbit (voice) (uncredited)