Giustino made his Grand Slam debut at the 2020 Australian Open.

He defeated Frenchman Corentin Moutet 0–6, 7–6 (7), 7–6 (3), 2–6, 18–16 in the first round of 2020 French Open as a first time main draw qualifier at this Major.

The match was the second-longest in French Open history, lasting 6 hours, 5 minutes.

[3] He qualified for his first ATP 500 tournament at the 2021 Dubai Tennis Championships as a lucky loser receiving a bye into the second round after the withdrawal of tenth seed Borna Ćorić.

This biographical article relating to Italian tennis is a stub.