The two mall operators are among the largest in the United States.
Simon is offering $91 per share in cash and stock for each share of Macerich. That represents a premium of 30 percent to the closing price of the mall operator's shares on Nov. 18, before Simon disclosed that it had accumulated a nearly 4 percent stake in Macerich.
The deal is valued at about $22.4 billion, counting debt.
Indianapolis-based Simon says it is confident that Macerich shareholders will accept its proposal.
A representative of Santa Monica, California-based Macerich did not immediately return a call from The Associated Press seeking comment.