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 and his favourite food is pizza. He became a father to a son in 2019.

Struff achieved his career-high No. 29 on 31 August 2020 after reaching Cincinnati QF. He peaked at No. 21 in doubles on 22 October 2018 soon after winning 1st doubles title at Tokyo w/McLachlan. He owns 3 ATP Tour doubles titles in 6 finals, but still seeking 1st singles final. Owns 0-7 record in SFs. He earned 1st tour-level win at 2013 Wimbledon as Q (d. Kavcic). He defeated Coric 11-9 in 5th to reach 2019 Roland Garros 4R. Advanced to 3R at 2018 Wimbledon, 2018 US Open and 2019 Wimbledon. In 2018, became 1st player in Open Era to rally from 2 sets down in 1R and 2R at Wimbledon (d. L. Mayer and Karlovic). He reached R16 at 8 ATP Masters 1000 events, including 2016 Paris as Q and 2019 Indian Wells. Saved 1 MP vs. No. 3 Wawrinka in Paris 2R and defeated No. 3 A. Zverev in Indian Wells 3R for biggest wins of career.

His coach is Carsten Arriens. His fitness trainer is Uwe Liedtke.