2015: ATP debut

Galán made his ATP main draw singles debut at the 2015 Claro Open Colombia where he was given a wildcard. He defeated Pere Riba in the first round.^[4]

2020: Grand Slam debut and third round at the French Open

Galán gained additional recognition after his 2020 French Open third round match with Novak Djokovic, his best showing at a Grand Slam thus far. He lost in straight sets (6–0, 6–3, 6–2), but his performance earned him new followers.^{[citation needed]}

2021: Masters 1000 debut and third round, Olympics debut

As a result of his first and best Masters 1000 third round showing thus far at the 2021 Miami Open, he reached a career-high of World No. 110 on 5 April 2021.

Galán qualified to represent Colombia at the 2020 Summer Olympics where he was defeated by World No. 5 and eventual Olympic champion Alexander Zverev in the second round.

2022: Wimbledon & US Open third rounds, first top-5 win, top 75

At the 2022 Córdoba Open he reached his first ATP quarterfinal of the year as a lucky loser where he lost to top seed Diego Schwartzman.

After missing three major events, he returned to the 2022 Wimbledon Championships where he reached the second round for a second consecutive year defeating Dominik Koepfer. He moved to the third round for the first time at this Major after the withdrawal of 17th seed Roberto Bautista Agut due to a positive COVID-19 test.^[5]

He reached the top 100 at World No. 99 on 25 July 2022, after a second round showing as a qualifier at the 2022 Hamburg European Open defeating Federico Coria. At the 2022 Croatia Open Umag he defeated 2016 champion Fabio Fognini.^[6]

He made his debut at the US Open as a qualifier.^[7] In the first round, he upset world No. 5 Stefanos Tsitsipas to advance to the second round, recording his first victory over a Top-5 player and for Colombia since Iván Molina took down then-No. 3 Manuel Orantes in Tehran in 1975.^[8] He became only the third player in the last five years to win a set 6–0 against him.^{[citation needed]} Although Tsitsipas saved eight match points, Galán capitalised on his ninth.^[9][10][11] He defeated Jordan Thompson in the second round in five sets to reach the third round at this Major for the second time in his career.^[12] As a result, he moved into the top 75 in the rankings.

At the 2022 San Diego Open he reached his second quarterfinal of the season defeating fourth seed Pedro Martínez (tennis)^[13] before losing to fifth seed and eventual champion Brandon Nakashima.^[14] As a result, he moved to the top 70 in the rankings No. 69 on 26 September.

He achieved an ATP career-high singles ranking of No. 67 on 28 November 2022.

2023: Wimbledon fourth round, top 60

In April, Galan reached the final at the 2023 Sarasota Open where he was the defending champion but lost to Daniel Altmaier.^[15]

At the 2023 Mutua Madrid Open in the first round, he played in the longest tiebreak of the ATP season thus far, falling 17-15 in 25-minutes to Alexander Bublik.^[16]

At the 2023 Wimbledon Championships he upset 24th seed Yoshihito Nishioka.^[17] Next he defeated qualifier Oscar Otte to reach a second consecutive third round. He defeated Mikael Ymer to reach his first fourth round at this Major and in his career. As a result, he moved to a new career high in the top 56 in the rankings on 17 July 2023.

2024: First Australian Open win

At the 2024 Australian Open, Galan needed almost five hours to the minute to win his first round match at this Major over local wildcard Jason Kubler.^[18] In Buenos Aires he recorded his second win of the season over wildcard Diego Schwartzman.

At the 2024 U.S. Men's Clay Court Championships he set a record in the history of the tournament, by winning the longest tiebreak 15-13 in the first set on his 10th set point, defeating Benoit Paire in straight sets in his first round match.^[19]

Singles: 19 (8–11)

More information Result, W–L ...

Result	W–L	Date	Tournament	Tier	Surface	Opponent	Score
Win	1–0	Jun 2015	Mexico F8, Manzanillo	Futures	Hard	Felipe Mantilla	6–3, 7–6(7–4)
Loss	1–1	Jul 2015	Colombia F4, Popayán	Futures	Hard	Eduardo Struvay	6–3, 6–7(5–7), 6–7(2–7),
Win	2–1	Oct 2015	Colombia F8, Bogotá	Futures	Clay	Cristian Rodríguez	6–3, 3–2 Retired
Loss	2–2	Oct 2016	Colombia F4, Valledupar	Futures	Hard	Marcelo Tomás Barrios Vera	6–4, 3–6, 6–7(5–7)
Loss	2–3	Oct 2016	Colombia F5, Manizales	Futures	Clay	Alejandro Gómez	6–7(4–7), 4–6
Loss	2–4	Oct 2016	Colombia F6, Neiva	Futures	Clay	Alejandro Gómez	5–7, 4–6
Loss	2–5	Nov 2016	Colombia F8, Medellín	Futures	Clay	Alejandro Gómez	7–5, 2–6, 6–7(3–7)
Loss	2–6	Dec 2016	Colombia F9, Villavicencio	Futures	Clay	Nicolas Santos	4–6, 2–6
Win	3–6	Jul 2017	Colombia F1, Valledupar	Futures	Hard	Christopher Díaz Figueroa	6–3, 7–5
Loss	3–7	Jul 2017	Colombia F2, Manizales	Futures	Hard	Facundo Argüello	4–6, 7–5, 2–6
Loss	3–8	Sep 2017	Bogotá, Colombia	Challenger	Clay	Marcelo Arévalo	5–7, 4–6
Win	4–8	Dec 2017	Peru F1, Lima	Futures	Clay	Nicolás Álvarez	7–5, 6–3
Win	5–8	Jul 2018	San Benedetto del Tronto, Italy	Challenger	Clay	Sergio Gutiérrez Ferrol	6–2, 3–6, 6–2
Loss	5–9	Feb 2020	Newport Beach, USA	Challenger	Hard	Thai-Son Kwiatkowski	4–6, 1–6
Win	6–9	Nov 2020	Lima, Peru	Challenger	Clay	Thiago Agustin Tirante	6–1, 3–6, 6–3
Loss	6–10	May 2021	Heilbronn, Germany	Challenger	Clay	Bernabé Zapata Miralles	3–6, 4–6
Win	7–10	Jan 2022	Concepción, Chile	Challenger	Clay	Santiago Rodríguez Taverna	6–1, 3–6, 6–3
Win	8–10	Apr 2022	Sarasota, USA	Challenger	Clay	Steve Johnson	7–6(9–7), 4–6, 6–1
Loss	8–11	Apr 2023	Sarasota, USA	Challenger	Clay	Daniel Altmaier	7–6(7–1), 6–1

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Doubles: 3 (2–1)

More information Result, W–L ...

Result	W–L	Date	Tournament	Tier	Surface	Partner	Opponents	Score
Win	1–0	Aug 2017	Colombia F3, Pereira	Futures	Clay	José Olivares	Christopher Díaz Figueroa Luis Patiño	6–2, 6–3
Loss	1–1	Aug 2017	Santo Domingo, Dominican Republic	Challenger	Clay	Santiago Giraldo	Juan Ignacio Londero Luis David Martínez	4–6, 4–6
Win	2–1	Dec 2017	Peru F1, Lima	Futures	Clay	João Pedro Sorgi	Boris Arias Federico Zeballos	4–6, 6–4, [10–3]

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Wins over top 10 players

• He has a 1–4 (20.0%) record against players who were, at the time the match was played, ranked in the top 10.

More information #, Player ...

#	Player	Rank	Event	Surface	Rd	Score	DEGR
2022
1.	Stefanos Tsitsipas	5	US Open, United States	Hard	1R	6–0, 6–1, 3–6, 7–5	94

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*As of 23 March 2024^[update]