Dr Sarah Wollaston, who practices in nearby Chagford, was the nomination in an 'open primary' that attracted nearly 16,500 votes.
She will contest the seat when its current MP, Anthony Steen, steps down at the next election.
Dr Wollaston told the BBC that her election campaign would focus on community hospitals, local healthcare and solutions for alcohol-related crime and violence.
All the constituency's voters were invited to participate in the US-style primary election.
The GP, the only candidate standing who was not a professional politician, received 7,914 votes. Her nearest rival, Sara Randall-Johnson, received 5,495.
Totnes has been a Conservative seat for all but one of the last 120 years, making it likely that Dr Wollaston will be elected next year.
Anthony Steen has held the seat since 1983. But he was forced to step down following the expenses scandal, during which he accused the public of jealousy about his 'very, very large house'.
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