MSP Keith Brown, councillor Christopher McEleny and activist Julie Hepburn are competing to replace Angus Robertson in the role.
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.
Ballots opened on May 18, with voters asked to rank candidates in order of preference under the single transferable vote system.
A series of hustings events were held across Scotland, with the three candidates putting their arguments forward to local members.
The candidates’ views on the timing of a second independence referendum were highlighted during the contest, with Mr McEleny using his candidacy to call for a new referendum inside the next 18 months.
Ms Hepburn, who campaigned for internal reforms in the party, said a second vote should take place before the next Holyrood elections in 2021 while Mr Brown said the timing depended on clarity on Brexit.