Paul Edward Valentine Giamatti (New Haven, 6 juni 1967) is een Amerikaans acteur, in 2005 genomineerd voor een Academy Award voor Beste Mannelijke Bijrol.

Giamatti's carrière begon in de jaren 90. Hij speelde voornamelijk bijrolletjes. Na de eeuwwisseling is Giamatti ook steeds vaker te zien in de hoofdrol. Zijn bekendste rollen zijn die van Harvey Pekar in American Splendor, Miles Raymond in Sideways, Joe Gould in Cinderella Man en Chuck Rhoades in Billions.

Giamatti is de jongere broer van acteur Marcus.

Filmografie 
She'll Take Romance (1990) (tv)... Heckler #2
Past Midnight (1992)... Larry Canipe
Singles (1992)... Kissing Man
NYPD Blue (1994)... Man In Sleeping Bag (episode "You Bet Your Life")
Mighty Aphrodite (1995)... Extras Guild Researcher
New York News (1995)... Dr. Wargner (episode "Past Imperfect")
Sabrina (1995)... Scott
Ripper (1996)... Dr. Bud Cable (video game)
Before and After (1996)... Courtroom Audience (uncredited)
The Show (1996)... Jeffrey Roffman (pilot episode)
Breathing Room (1996)... George
Arresting Gena (1997)... Detective Wilson
Donnie Brasco (1997)... FBI Technician
Private Parts (1997)... Kenny "Pig Vomit" Rushton
My Best Friend's Wedding (1997)... Richard the Bellman
Deconstructing Harry (1997)... Professor Abbot
A Further Gesture (1997)... Hotel Clerk
Homicide: Life on the Street (1998)... Harry Tjarks (episode "Pit Bull Sessions")
Tourist Trap (1998) (tv)... Jeremiah Piper
The Truman Show (1998)... Control Room Director
Dr. Dolittle (1998)... Blaine (uncredited)
Saving Private Ryan (1998)... Sergeant Hill
The Negotiator (1998)... Rudy Timmons
Safe Men (1998)... Veal Chop
Winchell (1998) (tv)... Herman Klurfeld
Cradle Will Rock (1999)... Carlo
Man on the Moon (1999)... Bob Zmuda/Tony Clifton
If These Walls Could Talk 2 (2000) (tv)... Ted Hedley (segment "1961")
Big Momma's House (2000)... John
Duets (2000)... Todd Woods
King of the Hill (2001)... Mr. McKay (episode "It's Not Easy Being Green")
Storytelling (2001)... Toby Oxman (segment "Non-Fiction")
Planet of the Apes (2001)... Limbo
Big Fat Liar (2002)... Marty Wolf
Thunderpants (2002)... Johnson J. Johnson
American Splendor (2003)... Harvey Pekar
Confidence (2003)... Gordo
The Pentagon Papers (2003) (tv)... Anthony Russo
Paycheck  (2003)... Shorty
Sideways (2004)... Miles Raymond
Saturday Night Live (2005)... Host (episode 30.10)
Robots  (2005)... Tim the Gate Guard (voice)
The Fan and the Flower (2005)... Narrator
Cinderella Man (2005)... Joe Gould
The Hawk Is Dying (2005)... George Gattling
Asterix and the Vikings (stem van Asterix in de Engelstalige versie, 2006)
The Illusionist (2006)... Chief Inspector Uhl
Lady in the Water (2006)... Cleveland Heep
The Ant Bully (2006)... Stan Beals (voice)
The Amazing Screw-On Head (2006) (tv)... Screw-On Head (voice)
Shoot Em' Up (2007)... Mr. Hertz
The Nanny Diaries (2007)... Mr. X
Too Loud a Solitude (2007)... Hanta (stem)
Fred Claus (2007)... Santa Claus
Pretty Bird (2007)... Rick Honeycutt 
John Adams (2007)... John Adams
Cold Souls (2009)... Giamatti, Paul
Duplicity (2009)... Richard Garsik
The Last Station (2009)... Vladimir Chertkov
The Haunted World of El Superbeasto (2009)... Dr. Satan (stem)
Barney's Version (2010)... Barney Panofsky
The Hangover: Part II (2011)... Kingsley
Win Win (2011)... Mike Flaherty
The Ides of March (2011)... Tom Duffy
Ironclad (2011)... King John
12 Years a Slave (2013)... Theophilus Freeman
Romeo & Juliet (2013)... Friar Lawrence
Saving Mr. Banks (2013)... Ralph
Downton Abbey (2013)... Harold Levinson
The Amazing Spider-Man 2 (2014)... Aleksei Sytsevich / Rhino
Madame Bovary (2014)... Monsieur Homais
Love & Mercy (2014)... Dr. Eugene Landy
Hoke (2014) (tv)... Hoke Mosely
The Little Prince (2015)... The Academy Teacher (stem)
San Andreas (2015)... Lawrence
Straight Outta Compton (2015)... Jerry Heller
Private Life (2018) - Richard
The Catcher Was a Spy (2018) - Samuel Goudsmit
Jungle Cruise (2021) - Nilo
Gunpowder Milkshake (2021) - Nathan

Amerikaans filmacteur