After surviving a difficult series of matches in group play and a close call in the semifinals, May-Treanor and Walsh Jennings enjoyed a relatively easy victory in the finals over fellow-Americans April Ross and Jennifer Kessy.
It was a 21-16, 21-16 decision and it left them with three of the five gold medals that have been awarded in the sport since it became a part of the Olympic program at the Atlanta Games in 1996.
May-Treanor, 35, and Walsh Jennings 33, have played together in 21 Olympic matches during their careers. They have won them all and in the process dropped only a single set.
They had to battle back in the opening set of the semifinals on Tuesday against the Chinese team of Xue Chen and Zhang Xi but ultimately prevailed 22-20, 22-20.
The first set of Wednesday's match was tied at 13-13 before May-Treanor and Walsh Jennings began to pull away. In the second set the eventual winners won three points in a row to take an 18-14 lead.
In the bronze medal match, Brazilians Larissa Franca and Juliana Silva rallied from a one-sided setback in the first set to defeat Xue and Zhang for third place.