He has performed as soloist with all the major orchestras in New Zealand. With the NZSO he has performed Sibelius, Lalo, Mozart and Bach concertos as well as works by leading New Zealand composers. As a soloist with the NZSO he has also recorded works by Lyell Cresswell and Ken Young.
Internationally, Leppänen has performed as a soloist and chamber musician in Australia, China, Japan, Philippines and Scandinavia. In 2005 he led the NZSO on its European/Japanese Tour and again in 2010 including unforgettable performances in the Musikverein in Vienna and Lucerne Festival Hall. On both of those tours he was also featured as a soloist. He has worked alongside internationally renowned soloists Hilary Hahn, Lang Lang, Pinchas Zukerman and Janine Jansen, to name a few. He has also appeared as guest concertmaster with the Melbourne Symphony Orchestra, Sydney Symphony, Japan Philharmonic, Tasmanian Symphony and Avanti! Chamber Orchestra. He's also a member of Irons/Leppanen/Joyce piano trio, which performs regularly Leppänen teaches at the New Zealand School of Music and has given masterclasses and coached the NZSO National Youth Orchestra and the Asian Youth Orchestra. He is also a Jury member in the Michael Hill International Violin Competition.