John Alden Thayer (December 22, 1857 – July 31, 1917) was a Representative from Massachusetts.

He was admitted to the bar in 1889 and was a clerk of the central district court of Worcester from 1892 to 1897.

He failed reelection in 1912 to the Sixty-third Congress.

In 1915, he was appointed postmaster of Worcester, and served until his death.

In mid July 1917 Thayer was admitted into the Peter Bent Brigham Hospital in Boston where he died on July 31, 1917.