2011

Withrow competed at the 2011 US Open doubles tournament, where he received together with his partner Jack Sock a wildcard. In the first round they were beaten by 15-seeded Xavier Malisse from Belgium and Mark Knowles from the Bahamas.^[1]

2016

At the 2016 NCAA Men's Tennis Championship, Withrow and Texas A&M Aggies teammate Arthur Rinderknech lost the individual doubles championship to UCLA's Mackenzie McDonald and Martin Redlicki in the final match.

2017: First ATP win in doubles

Withrow and Sock received a wildcard for the 2017 Cincinnati Masters doubles tournament, where they lost to Juan Sebastián Cabal and Fabio Fognini in the first round.

He won his first ATP level doubles match with partner Austin Krajicek at the 2017 US Open by defeating Philipp Oswald and André Sá in the first round.

2018: First ATP doubles title

Withrow and Sock made a doubles run to the title at the 2018 Delray Beach Open, first defeating Leander Paes and Purav Raja in the first round. Next the pair upset the Bryan brothers in the quarterfinals in 3 sets, then won their next match to set up a finals match against Nicholas Monroe and John-Patrick Smith. Withrow and Sock prevailed in three sets to win the tournament, marking Withrow's first ever ATP tour-level title as well as his first doubles title.

2019: US Open quarterfinal in doubles

At the 2019 Australian Open he reached the third round with Jack Sock, defeating second seeded pair and previous year finalists Juan Sebastián Cabal / Robert Farah (tennis) on the way.^[2]

At the 2019 US Open, partnering Sock, he reached his first Grand Slam quarterfinal defeating the Bryan brothers en route but lost to 15th seeded pair of Jamie Murray/Neal Skupski.

2020–21: New partnership with Lammons, Win over World No. 1 doubles team

He reached a career-high doubles ranking of World No. 66 on January 13, 2020.

At the 2021 US Open partnering Nathaniel Lammons they defeated top pair Nikola Mektić and Mate Pavić in the first round in 75 minutes.^[3]

2022: Second ATP title, top 50 debut

At the 2022 San Diego Open he won his first ATP title as a team with Lammoms.^[4] The pair moved up 25 places to 35th in the doubles race. He made his top 50 debut in the rankings on 26 September 2022.

The pair Withrow/Lammons ended the season at No. 32 in the ATP doubles rankings.

2023: Four titles, Four finals, Masters semifinal, top 25

With Lammons, Withrow reached three finals in Auckland, in Dallas and at the ATP 500 Mexican Open in Acapulco.^[5][6]

The pair won the Challenger title at the 2023 Arizona Tennis Classic. At the 2023 Miami Open they reached the semifinals of a Masters for the first time but lost to eventual champions Santiago González and Édouard Roger-Vasselin.^[7]

Withrow reached the top 25 on 16 October 2023. The pair reached their eight final for the season and second at the ATP 500 level at the 2023 Erste Bank Open in Vienna.

At the last Masters of the season in Paris the pair reached the quarterfinals defeating sixth seeds Máximo González and Andrés Molteni.^[8]

Doubles: 12 (6 titles, 6 runner-ups)

Result	W–L	Date	Tournament	Tier	Surface	Partner	Opponents	Score
Loss	0–1	Feb 2018	Ecuador Open, Ecuador	250 Series	Clay	Austin Krajicek	Nicolás Jarry Hans Podlipnik Castillo	6–7(6–8), 3–6
Win	1–1	Feb 2018	Delray Beach Open, United States	250 Series	Hard	Jack Sock	Nicholas Monroe John-Patrick Smith	4–6, 6–4, [10–8]
Win	2–1	Sep 2022	San Diego Open, United States	250 Series	Hard	Nathaniel Lammons	Jason Kubler Luke Saville	7–6(7–5), 6–2
Loss	2–2	Oct 2022	Gijón Open, Spain	250 Series	Hard (i)	Nathaniel Lammons	Máximo González Andrés Molteni	7–6(8–6), 6–7(4–7), [5–10]
Loss	2–3	Jan 2023	Auckland Open, New Zealand	250 Series	Hard	Nathaniel Lammons	Nikola Mektić Mate Pavić	4–6, 7–6(7–5), [6–10]
Loss	2–4	Feb 2023	Dallas Open, United States	250 Series	Hard (i)	Nathaniel Lammons	Jamie Murray Michael Venus	6–1, 6–7(4–7), [7–10]
Loss	2–5	Mar 2023	Mexican Open, Mexico	500 Series	Hard	Nathaniel Lammons	Alexander Erler Lucas Miedler	6–7(9–11), 6–7(3–7)
Win	3–5	Jul 2023	Hall of Fame Open, United States	250 Series	Grass	Nathaniel Lammons	William Blumberg Max Purcell	6–3, 5–7, [10–5]
Win	4–5	Jul 2023	Atlanta Open, United States	250 Series	Hard	Nathaniel Lammons	Max Purcell Jordan Thompson	7–6(7–3), 7–6(7–4)
Win	5–5	Sep 2023	Winston-Salem Open, United States	250 Series	Hard	Nathaniel Lammons	Lloyd Glasspool Neal Skupski	6–3, 6–4
Win	6–5	Sep 2023	Astana Open, Kazakhstan	250 Series	Hard	Nathaniel Lammons	Mate Pavić John Peers	7–6(7–4), 7–6(9–7)
Loss	6–6	Oct 2023	Vienna Open, Austria	500 Series	Hard (i)	Nathaniel Lammons	Rajeev Ram Joe Salisbury	4–6, 7–5, [10–12]

Doubles: 24 (17–7)

Result	W–L	Date	Tournament	Tier	Surface	Partner	Opponents	Score
Win	1–0	Jul 2016	USA F25, Edwardsville	Futures	Hard	Connor Smith	Luke Bambridge Marc Polmans	6–3, 6–2
Loss	1–1	Sep 2016	Canada F7, Toronto	Futures	Clay	Hunter Reese	Hans Hach Rhyne Williams	5–7, 4–6
Loss	1–2	Oct 2016	USA F31, Houston	Futures	Hard	Hunter Reese	Hans Hach Rhyne Williams	3–6, 3–6
Win	2–2	Jan 2017	USA F2, Long Beach	Futures	Hard	Austin Krajicek	Luke Bambridge Joe Salisbury	6–3, 3–6, [10–8]
Win	3–2	Jan 2017	Maui, USA	Challenger	Hard	Austin Krajicek	Bradley Klahn Tennys Sandgren	6–4, 6–3
Win	4–2	Feb 2017	Morelos, Mexico	Challenger	Hard	Austin Krajicek	Kevin King Dean O'Brien	6–7(4–7), 7–6(7–5), [11–9]
Win	5–2	Jul 2017	USA F21, Tulsa	Futures	Hard	Austin Krajicek	Tommy Paul Nathan Ponwith	6–4, 6–2
Win	6–2	Jul 2017	Gatineau, Canada	Challenger	Hard	Bradley Klahn	Hans Hach Vincent Millot	6–2, 6–3
Win	7–2	Jul 2017	Granby, Canada	Challenger	Hard	Joe Salisbury	Marcel Felder Go Soeda	4–6, 6–3, [10–6]
Loss	7–3	Nov 2017	Shenzhen, China, P.R.	Challenger	Hard	Austin Krajicek	Sriram Balaji Vishnu Vardhan	6–7(3–7), 6–7(3–7)
Loss	7–4	Nov 2017	Hua Hin, Thailand	Challenger	Hard	Austin Krajicek	Sanchai Ratiwatana Sonchat Ratiwatana	4–6, 7–5, [5–10]
Win	8–4	Mar 2018	Indian Wells, USA	Challenger	Hard	Austin Krajicek	Evan King Nathan Pasha	6–7(3–7), 6–1, [11–9]
Win	9–4	Jun 2019	Columbus, USA	Challenger	Hard (i)	Roberto Maytín	Hans Hach Donald Young	6–7(4–7), 7–6(7–2), [10–5]
Loss	9–5	Aug 2019	Lexington, USA	Challenger	Hard	Roberto Maytín	Diego Hidalgo Martin Redlicki	2–6, 2–6
Win	10–5	Sep 2019	Columbus, USA	Challenger	Hard	Martin Redlicki	Nathan Pasha Max Schnur	6–4, 7–6(7–4)
Loss	10–6	Nov 2020	Orlando, USA	Challenger	Hard	Mitchell Krueger	Andrey Golubev Aleksandr Nedovyesov	5–7, 4–6
Win	11–6	Mar 2021	Nur-Sultan, Kazakhstan	Challenger	Hard (i)	Nathaniel Lammons	Nathan Pasha Max Schnur	6–4, 6-2
Win	12–6	May 2021	Heilbronn, Germany	Challenger	Clay	Nathaniel Lammons	André Göransson Sem Verbeek	6–7(4–7), 6–4, [10–8]
Win	13–6	Nov 2021	Champaign, USA	Challenger	Hard (i)	Nathaniel Lammons	Treat Huey Max Schnur	6–4, 3–6, [10–6]
Loss	13–7	Feb 2022	Cleveland, USA	Challenger	Hard (i)	Robert Galloway	William Blumberg Max Schnur	3–6, 6–7(4–7)
Win	14–7	Apr 2022	Sarasota, USA	Challenger	Clay	Robert Galloway	André Göransson Nathaniel Lammons	6–3, 7–6(7–3)
Win	15–7	Jul 2022	Salzburg, Austria	Challenger	Clay	Nathaniel Lammons	Alexander Erler Lucas Miedler	7–5, 5–7, [11–9]
Win	16–7	Sep 2022	Cary, USA	Challenger	Hard	Nathaniel Lammons	Treat Huey John-Patrick Smith	7–5, 2–6, [10–5]
Win	17–7	Mar 2023	Phoenix, USA	Challenger	Hard	Nathaniel Lammons	Hugo Nys Jan Zieliński	6–7(1–7), 6–4, [10–8]