The 170-meter tower on the National Mall in Washington, D.C. was shut down on August 17 following repeated problems with the structure's elevator, Efe news reported on Saturday.
Financier and philanthropist David Rubinstein has agreed to provide up to $3 million for a major upgrade to the elevator.
Although funding for the elevator overhaul is secured, there was no date set for the start of the work, according to The Washington Post.
The Park Service is awaiting congressional approval of funding for a new security screening facility at the site.
Work on the monument to honour first American President George Washington, got under way in 1848 and the obelisk was dedicated in 1885.
The Washington Monument receives more than 500,000 visitors a year.