Констант Лестиен

2015: ATP Tour debut

Lestienne reached his first career ATP Tour singles main draw at the 2015 Estoril Open after winning two singles qualifying matches. He lost in the first round to Pablo Carreño Busta.

2016: First challenger title, betting scandal and ban

In May 2016, Lestienne won his first ATP Challenger Tour tournament in Ostrava.

In September 2016, Lestienne was suspended for seven months and fined $10,000 by the International Tennis Federation for betting on tennis matches. The Tennis Integrity Unit (TIU) in cooperation with French online gambling regulator ARJEL found that Lestienne had bet on 220 tennis matches from February 2012 to June 2015. None of these matches were his own. Half of the ban was suspended, and his fine would be cut in half if he assisted the TIU.

2017: Grand Slam debut in doubles

He made his Grand Slam main draw debut at the 2017 French Open after receiving a wildcard to the doubles main draw with Corentin Moutet. They defeated Dustin Brown and Lu Yen-hsun in the first round, but were defeated by Jean-Julien Rojer and Horia Tecău in the second round.

2021-2022: Four Challengers, Top 75, first ATP semifinal

He won his third Challenger at the 2021 JC Ferrero Challenger Open in Alicante, Spain in October 2021. As a result, he climbed 50 positions in the rankings to world No. 208 on 18 October 2021.

On August 1, 2022, Lestienne entered the Top 100 at World No. 90, following two ATP Challenger Tour titles in Spain in July 2022 and two more finals in the same year. He won his third Challenger in Vancouver in August and reached the top 75 in the rankings on 22 August 2022.

In September 2022, Lestienne reached his first quarterfinal on the ATP Tour at the San Diego Open defeating Brandon Holt and sixth seed Alejandro Tabilo. He entered the top 70 in the rankings on 26 September 2022 at world No. 68. Lestienne followed this by reaching his first semifinal at the 2022 Tel Aviv Open defeating seventh seed compatriot Adrian Mannarino, Emil Ruusuvuori and fourth seed Maxime Cressy in the quarterfinal, his first win against a player in the Top 50.

2023: Major & Masters singles debuts, first Major win & top 50

At 30 years old, he made his Grand Slam debut in singles at the 2023 Australian Open and won his first Major match defeating Thiago Monteiro. He reached the top 50 on 6 February 2023 at world No. 48.

In February, Lestienne reached his first ATP Tour doubles final at the Qatar Open, playing along Botic van de Zandschulp losing to Rohan Bopanna and Matthew Ebden in the finals.

He made his Masters debut at the 2023 Indian Wells Masters but retired in the first round against Emil Ruusuvuori. He also made his debut at the Italian Open but also retired after one set in the first round against Laslo Djere. On his debut at the 2023 French Open he lost in the first round to 11th seed Karen Khachanov. Also on his debut at Wimbledon he lost in the first round to Liam Broady.

In August, Lestienne won the title in Stanford, defeating qualifier Emilio Nava in the final, his first Challenger title in a year. In September, Lestienne won another Challenger title in Saint-Tropez, defeating ninth seed Liam Broady in the final, returning in the top 100 on 25 September 2023 as a result. In October, Lestienne reached his 14th Challenger final in Alicante and defeated fellow countryman Hugo Grenier in the final for a second time at this tournament, winning his ninth Challenger.