Cachin made his ATP main-draw debut as a wildcard in the doubles competition of the 2015 Argentina Open, partnering Facundo Argüello.

They saved a match point and defeated the second-seeded pair of Máximo González and Horacio Zeballos before losing to Carlos Berlocq and Diego Schwartzman in the second round.

Cachin entered his first Grand Slam tournament at the 2015 Wimbledon Championships, but was eliminated by Jimmy Wang 4–6, 6–3, 7–5 in the first round of the qualifying competition.

In 2020, Cachin won the World Tennis Tour title in Paguera, Spain, beating Matthieu Perchicot in the final.

In 2021, Cachin won the 2021 Open de Oeiras II, beating Nuno Borges in the final for his second Challenger title.

In January, Cachin reached the second round of qualifying at the Australian Open, defeating ninth seed Francisco Cerundolo before losing to Marco Trungelliti.

[2] Cachin qualified for the French Open as lucky loser to make his Grand Slam singles main-draw debut.

Cachin made his Masters debut at the BNP Paribas Open and won his first match at this level over Nikoloz Basilashvili.

[8] In July, Cachin won his maiden ATP title in Gstaad, where he defeated Albert Ramos Viñolas in the final in three sets.