The former agriculture and lands minister and caucus chairman suffered a heart attack last year, but returned to the legislature after his recovery.
Premier Christy Clark said in a statement that Cantelon leaves behind a legacy including improved access to health care, affordable housing and early learning programs in Parksville and Qualicum.
Cantelon first entered politics in 1999 when he was elected to serve on Nanaimo City council and jumped to provincial politics in 2005.
Cantelon's decision not to run in May adds to the more than one dozen Liberals, including former veteran cabinet ministers Kevin Falcon and George Abbott, who announced they won't be seeking re-election.
Clark said Cantelon helped develop the government's seniors' action plan while serving as the parliamentary secretary for seniors to the Minister of Health.
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