MSP Keith Brown, councillor Christopher McEleny and activist Julie Hepburn are competing to replace Angus Robertson in the role and have been taking part in hustings around the country.
Mr Brown, Scotland’s Economy Secretary, is the highest profile figure in the race, while Mr McEleny, leader of the SNP group on Inverclyde Council, competed in the previous depute leadership election.
While not an elected representative, Ms Hepburn is well known within the party.
The depute leader role became available when Mr Robertson stepped down in February after losing his Westminster seat in last year’s general election.
The party said around 100,000 members would qualify to be sent ballot papers and asked to rank candidates in order of preference under the single transferable vote system.
Voting closes on June 8, with the winner announced at the SNP conference in Aberdeen later that day.