The movie director, who has worked with Williams on films such as Jurassic Park and ET, said that the composer's musical scores have the power to go "right to your heart" when you listen to them.
Additional reporting by Chris Allen
"John and I have had a 40-year relationship this year, this is our 40th anniversary," Spielberg told journalists at the UK press conference for War Horse. "We started working together in 1972 on The Sugarland Express. We start our next score in about three months. Johnny scores Lincoln in three months and that will be our... God, we've been together a lot.
"John is the most important collaborator I've ever had in my career. He makes me look good, he makes my films look better. I get a lot of credit that should be going to John. but I've kept the people who have been in my career who I feel are my family."
Paying tribute to his frequent collaborators, Spielberg added: "[Producer] Kathy [Kathleen Kennedy] has been with me since 1978. Janusz Kamiński, my cinematographer, has made every movie with me since Schindler's List. Michael Kahn has cut every motion picture I've directed since 1976 when we made Close Encounters together. Rick Carter has done 15 of my directed films as a production designer.
"I really believe in the family of collaboration and so Johnny is certainly no less or no more important than the entire group of all of us, but Johnny does make a contribution that goes right to your heart. A lot of the contributions from my other collaborators are subliminal - you don't really single them out for credit.
"Without them, the films wouldn't have the impact they have, but John certainly has the most considerable impact because his music immediately bypasses the brain and goes straight to your heart. That's the way he's always been... an amazing talent."
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Watch Digital Spy speaking to stars on the red carpet at the War Horse premiere below: