Jan-Lennard began playing tennis at age 6 with his parents, Dieter and Martina, who are both tennis coaches. His favourite surface is clay, shot is backhand and tournament is Roland Garros. He lists Rome and Miami as his favourite cities on tour. Jan-Lennard is a big football fan who supports Borussia Dortmund. He became a father to a son in 2019. His coach is Carsten Arriens and his fitness trainer is Uwe Liedtke.

After a difficult 2022 season which saw him go down in the rankings due to an injury that kept him away from the courts for a while, Struffi made a sensational comeback in 2023. He started the year no.150 on the ATP Ranking making his way through the qualifying of the Australian Open, Indian Wells, Miami and Monte-Carlo beating world no.3 Casper Ruud to reach the Quarter-finals. In Madrid, Struffi beat Tsitsipas en route to reach his first final at a Masters 1000 event. In Stuttgart, made his second final of the season, his first on grass and reached a career-high ranking no.21 in the world.