Martin Damm Jr. (born September 30, 2003) is an American professional tennis player. He has a career-high ATP singles ranking of world No. 125 achieved on February 16, 2026 and a doubles ranking of No. 303 achieved on November 6, 2023.
On the junior tour, Damm has a career high junior ranking of No. 3, achieved on January 1, 2021.
In August 2019, Damm and his partner Toby Kodat won the USTA Boys 18s National Championships doubles title, earning the pair a wildcard entry into the doubles main draw of the 2019 US Open. Damm age 15 and fellow American Toby Kodat age 16 became the youngest men's doubles team to win a US Open match in the Open Era.
Damm received a wildcard into the qualifying draw of the 2022 Miami Open and the 2022 US Open.
He also entered the qualifying competitions at the 2023 Miami Open, and at the 2023 US Open as a wildcard.
In March, Damm was also awarded a main draw wildcard at the 2024 Miami Open for his Masters debut where he recorded his first ATP Tour and Masters level win over Zhizhen Zhang and 14th seed and compatriot Tommy Paul by retirement. As a result, he reached the top 175 in the rankings on 1 April 2024.
Ranked No. 431, Damm made his debut at the 2025 US Open, after making the main draw using a qualifying wildcard, and recorded his first major win over fellow American and wildcard Darwin Blanch.
Damm qualified for the main draw at the ATP 250 2026 Open Occitanie and upset seventh seed Hubert Hurkacz, and Roberto Bautista Agut in straight sets. He then downed Luca Nardi in the last eight to advance to his first ATP tour-level semifinal. As a result he reached a new career-high of No. 130 in the singles rankings, raising up 30 places, on 9 February 2025.
Damm is the son of Czech former professional tennis player Martin Damm, Sr., who reached world No. 5 in doubles. He has two other siblings.