Born in 1959 in Lacombe, Alberta, Sonmor studied art from 1983 to 1988 at the Alberta College of Art and Design in Calgary and at the Banff Centre for the Arts' summer studio program in 1986. His first solo exhibition was held at Truck Contemporary Art Gallery (Calgary) in 1988, and later that year he moved to Montreal, Quebec, to attend Concordia University. During 1990-1, solo exhibitions of his work were held at Modern Fuel Artist-Run Centre (Kingston ON) and Centre des arts actuels Skol (Montreal). After graduating from Concordia with a Masters of Fine Art in 1991, Sonmor remained in Quebec. In 1993 he exhibited at the parallel galleries, Langage Plus (Alma QC), and at the Niagara Artists Centre (St Catharines ON).
In 1998 the University of Waterloo organized an exhibition of Sonmor's work which toured the Art Gallery of Sudbury, and the Art Gallery of Algoma (Sault Ste Marie ON). In 2002, Sonmor participated with artists Peter Krausz and Tom Hopkins in the group show Made In Canada: Contemporary Art from Montreal at the Plattsburgh State Art Museum (Plattsburgh NY). A retrospective of his work, on display at the Mendel Art Gallery (Saskatoon SK), the Art Gallery of Southwestern Manitoba (Brandon MB) and the Robert McLaughlin Gallery (Oshawa ON) in 2002-3 and a solo exhibition at the Art Gallery of Mississauga in 2004 established his reputation across Canada In 2010 he exhibited with James Lahey and Ed Bartram at the Macdonald Stewart Art Centre (Guelph ON). In 2012 an exhibition with painter France Jodoin at the Musée des beaux-arts de Sherbrooke (Sherbrooke Museum of Fine Arts) drew positive media reviews. In 2014 a solo exhibition of his work was held at the Art Gallery of Grande Prairie (Grande Prairie AB). Throughout his career, solo exhibitions of his work were also held in private galleries across North America.