Monday's decree formalized Trump's statement last week, saying it was time for the US "to fully recognize" Israeli sovereignty over the Golan. The move appeared to give Netanyahu a boost before the closely contested April 9 Israeli elections.
"This was a long time in the making," Trump said alongside Netanyahu in the White House.
"Today, aggressive action by Iran and terrorist groups in southern Syria, including Hezbollah, continue to make the Golan Heights a potential launching ground for attacks against Israel - very violent attacks," Trump said. "This should have been done numerous presidents ago."
Israel seized much of the Golan Heights from Syria during the 1967 Six-Day War and then effectively annexed it in 1981, a move that was never recognized by the international community.