[5] Nagal won his 1st ever ITF Futures title by defeating Gustavo Vellbach 6–2, 6–0 at India F8 tournament.
Nagal won the 2015 Wimbledon boys' doubles title with his Vietnamese partner Lý Hoàng Nam, defeating Reilly Opelka and Akira Santillan in the final.
Nagal won Uzbekistan F1 with Ti Chen by defeating Sanjar Fayziev and Jurabek Karimov 5–5 ret.
Nagal made his Davis Cup debut for India in the 2016 World Group Playoff tie against Spain in New Delhi.
Nagal won gold medal at Asian Indoor and Martial Arts Games by defeating compatriot Vijay Natrajan 6–1,6-1 in the final.
Nagal made his Asian Games debut in 2018 edition, He competed in doubles event pairing with Ramkumar Ramanathan, They reached the Quarter-finals before losing to eventual silver medallists Alexander Bublik and Denis Yevseyev.
Nagal failed to win a single match in the qualifying rounds of any Grand Slam events, he missed US Open due to an injury.
Nagal then qualified for main draw of Barcelona Open after beating Illya Marchenko and Thomas Fabbiano.
[20] Nagal holds the distinction of being the first Indian in 25 years to reach the second round of an Olympics singles tennis event.
[22] But before he was injured he lastly played at Sibiu Challenger where he made it to the semi-finals before losing to top seed and eventual champion Stefano Travaglia.
He then lost to Gauthier Onclin in three sets in first qualifying round of the 2023 BW Open ending the first month of the year winless.
In February, Nagal reached his first challenger semifinal since Sibiu 2021 in Chennai after coming through qualifying, beating Calum Puttergill and Nam Ji-sung.
In the main draw, he beat 4th seed Ryan Peniston, lucky loser Jason Jung, and unseeded Jay Clarke, before losing to Nicolas Moreno de Alboran in the semifinals.
His success continued on clay, after reaching yet another semifinal in Tulln, defeating Albert Ramos-Viñolas for his first victory over a top 100 player on his way.
As an alternate in Helsinki, Nagal reached another challenger quarterfinal, his first on hard courts of the year, after beating Dennis Novak and Jakub Menšík.
In the semifinals, he defeated lucky loser Stefano Travaglia to reach his fourth Challenger final of the year.
Having been denied a wildcard to the 2024 Australian Open by the AITA for not participating in the Davis Cup, he qualified making his second appearance in the main draw at this Major after three years of absence.
[35] He qualified for his next Masters in Monte Carlo becoming the first Indian singles player in 42 years to make it to the main draw at this tournament.
In 2017, reports surfaced that Nagal had missed a practice session in July 2016 at Chandigarh during the tie against South Korea, citing elbow injury.
He was dropped from the Indian Davis Cup squad led by Anand Amritraj which was scheduled to face New Zealand between 3 and 5 February 2017.
A source close to All India Tennis Association (AITA) told Sportskeeda, "It is a case of sheer indiscipline, on the part of the player.
Because I have spent 2 weeks with Sumit in December helping him with his training and his rehab for the current shoulder injury he is recovering from.