Underhill travaille aussi beaucoup comme chef d’orchestre, particulièrement en musique contemporaine et en musique du début du XXe siècle. Il a dirigé le Turning Point Ensemble, l’Orchestre de la radio de Radio-Canada, l’Orchestre symphonique de Vancouver, et celui du Centre national des Arts, entre autres. Fervent défenseur des arts, il est engagé au sein de plusieurs organismes de musique canadienne.

As a composer, Underhill has a substantial catalogue of more than sixty-five works including an opera, large-scale works for dance, several works for orchestra, choral music, and a large body of chamber music for diverse groups. Among his most recent compositions are World of Light (2008) for tenor and orchestra, a clarinet quintet entitled Still Image (2007), A Middle English Songbook (2006) for choir and ensemble, and Canzone di Petra (2004), a piece for flute and harp which was the winner of the 2007 Western Canadian Music Outstanding Composition Award. In addition to The Faerie Queen, Underhill also co-wrote the score with Michael Bushnell for John Alleyne’s full-length narrative ballets Tristan and Isolde, premiered by the National Ballet of Canada in 2003, and Orpheus, premiered by Ballet British Columbia in 2002. Other works include the opera The Star Catalogues, written with librettist Marc Diamond and produced by Vancouver New Music in 1994; and the orchestral work Lines of Memory which won first prize in the 1994 du Maurier Canadian Composers’ Competition. His compositions have been performed by leading music organizations in Canada including Arraymusic, Quatuor Bozzini, the St Lawrence String Quartet, Esprit Orchestra, Vancouver Cantata Singers, Manitoba Chamber Orchestra, musica intima, the Vancouver Symphony, and the Turning Point Ensemble. Recent international performances have included the premiere of two new chamber works by the CrossSound Festival in Alaska, a Boston premiere by the King’s Chapel Choir and Arcadian Winds, and a performance of his One Page Sonata in Bratislava, Slovakia. His music is regularly broadcast on CBC, and has been included on several recordings including his disc Celestial Machine on the Artifact Music label. From that disc, the choral work Love Songs was nominated for a Juno in the category of Best Classical Composition in 2002.

As a conductor, Underhill has made conducting appearances with the Turning Point Ensemble, CBC Radio Orchestra, Manitoba Chamber Orchestra, the Victoria Symphony, the Vancouver Symphony, the National Arts Centre Orchestra, and the Vancouver New Music Ensemble. Underhill has been especially active in contemporary music and music of the early twentieth century. He has conducted premieres of orchestral pieces by such Canadian composers as Glenn Buhr, Michael Bushnell, Chan Ka-nin, Stephen Chatman, José Evangelista, Anthony Genge, Melissa Hui, Rudolf Komorous, David MacIntyre, Linda Catlin Smith, and Heather Schmidt. Canadian operas he has conducted include Nonomiya by Rudolf Komorous (premiere), the Banff Centre for the Arts production of Zurich 1916 by Christopher Butterfield and John Bentley Mays (premiere), Elsewhereless by Rodney Sharman and Atom Egoyan (Vancouver premiere), and Kopernikus by Claude Vivier, He has conducted works in collaboration with several prominent international composers including Louis Andriessen, Gavin Bryars, Sofia Gubaidulina, Giya Kancheli, James MacMillan, Steve Reich, Toru Takemitsu, and Judith Weir. Soloists he has worked with include François Houle, Shauna Rolston, Valdene Anderson, Jamie Parker, Lori Freedman, and Anssi Kartunen. His performances are regularly broadcast on the CBC. Underhill’s discography as a conductor includes a recording of the music of Gavin Bryars with the CBC Radio Orchestra (CBC Records), two discs with the Vancouver New Music Ensemble (Centrediscs and CBC Records), three recordings with the Turning Point Ensemble (Liquid on the ATMA label, Strange Sphere: music of Rudolf Komorous on the Artifact label, and Disasters of the Sun: music of Barbara Pentland on Centrediscs).

Active as a programmer and promoter of contemporary music, Underhill was Artistic Director of Vancouver New Music from 1987 to 2000, a period of substantial growth for the organization. He is currently Artistic Co-Director of the Turning Point Ensemble, a large chamber ensemble of outstanding Vancouver musicians dedicated to the celebration of twentieth century music and new music. He has been active as an arts advocate and supporter of Canadian music organizations, currently serving as the Vice-President of the Canadian Music Centre. Underhill has been an SFU faculty member since 1981, serving as Director of the School for the Contemporary Arts over an eight-year period. He is currently serving as Dean Pro Tem of the Faculty of Communication, Art and Technology.