Pitt praised the Pritzker Prize-winning architect at a planning consultation for Zumthor's LACMA project organised by the County of Los Angeles Board of Supervisors.
"There's no way to understand his work from a computer-generated image," said Pitt in defense of the project. "You really have to stand in them to see his mastery of light and shadow."
Pitt championed Zumthor as a guest speaker at the meeting, which was held to certify the Final Environmental Impact Report (FEIR) for the architect's scheme.
LA's board of supervisors also confirmed it will contribute $117.5 million (£89.56 million) towards the cost of the project, which is estimated to cost $560million (£428.7 million) in total.
LACMA approved despite criticisms
The environmental approval and financial boost mark a major step forward for the LACMA development, and comes in spite of severe opposition to Zumthor's proposal.
First unveiled in 2013, the David Geffen Galleries proposal was intended to allow LACMA to accommodate its growing collection. However the latest iteration, revealed by LACMA last month, is 10,000 square feet (929 square metres) smaller than the existing space.
"LACMA has become the Incredible Shrinking Museum," said Los Angeles Times art critic Christopher Knight. He critiqued the scheme in a piece that called for the board to not approve the environmental report.
"I couldn't name another art museum anywhere that has ever raised hundreds of millions of dollars to spend on reducing its collection space," said Knight.
As revealed in Knight's article the size of the LACMA proposal has varied since it was first revealed.
The original 2013 scheme comprised an undulating black form that matched the size of the current buildings. However a smaller, revised version that would bridge a road, was revealed one year later after concerns were raised that the building would damage the nearby La Brea Tar Pits.
The latest iteration is even smaller. Renderings released by LACMA show a curved structure elevated above ground atop a series of of semi-transparent pavilions.
LACMA will be Zumthor's first US project
This curvilinear upper level will have approximately 110,000 square feet (10,000 square metres) of galleries in a continuous space, not including the lower level.
An earlier design had a total of 37,000 square metres of exhibition spaces.
With the go-ahead now received, construction is slated to commence on Zumthor's LACMA galleries next year. Once complete, it will be his first building in the US.
Pitt's support forms ongoing fascination with architecture
Pitt's support of Zumthor's aesthetic is part of the actor's ongoing interest in architecture and design.
Pitt established housing charity Make it Right in 2006 to house people who lost their homes when Hurricane Katrina hit New Orleans.
The charity is now facing a lawsuit as residents reported water leaks, black mould, foundation issues and ill health.
Images are courtesy Peter Zumthor & Partner, unless stated otherwise.