Lehto began composing in the early 1980s with small-scale easy-listening pieces and with very practical pedagogical goals. In the 1990s, Lehto began to change his style and refine his skills by applying for private studies in composition (Kalevi Aho,Lauri Kilpiö). Lehto continued these and course-based studies(Jukka Tiensuu, Jouni Kaipainen) until spring 2016.

After becoming a member of the Finnish Composers’ Association in 1999, Lehto was encouraged to try composing for a symphony orchestra. The premiere of a commissioned work written for Pori’s new concert hall called “Promenadi” in early 2000 was a significant turning point in his career. In addition to domestic success, the work became one of his most played abroad. At the same time, commissions for chamber and orchestral music began to appear alongside commissions for wind orchestras, and this development can be considered to have culminated in 2015, when Lehto was chosen as one of the composers of the nationwide “Sibelius Followers” funding project. For the composer, this project culminated in the premiere of the orchestral work “My City” played by Pori Sinfonieta.

Alongside the orders, participation in various composition competitions took place all the time. In addition to domestic prize places, Lehto has three wins in the international composition competition in this area. Based on the competition wins “Ciutat de Betera” 2009 and “Riga Windstream” 2014 as well as significant pedagogical flute music production, the Satakunta Arts Council awarded Lehto the Satakunta Art Prize in 2014. In the spring of 2018, Lehto was awarded the first prize in the “elementary” series of the EDR Foundation (USA) piano composition competition. His latest competition success is from 2021: the second prize was awarded in the Tampere Piano Society’s composition competition for the Tampere Piano Competition 2021.
Lehto’s works are published or released in Finland by Edition Musact, SULASOL and MusicFinland and abroad, Belgian Metropolis-music, Spanish Periferia Music and Leading tones in USA. As a composer in concert Lehto has visited Estonia, Latvia, Austria, Norway, Belgium, England, Spain, USA, Japan and Italy.

Recent premieres have included “Mundus sonialis” for four cellos and orchestra (August 2020, Pori) and the online work “KOTA” for flute and synthetic ensemble (February 2021). The flute sonata ”Script” premiered in may 2023 at the Tokyo Spring Festival. A piece for soprano and chamber ensemble, ”Som snö”(like the snow) got the premiere in december 2023. On May 2024, Lehto’s composition concert featured his chamber and piano music
as well as the premiere of his string quartet ”Fantaisie”. In January 2025, Lehto’s new work ”Penelope” for chamber ensemble premiered in Helsinki at Finland’s most important contemporary music festival, Musica Nova.