Angus Robertson said the SNP must focus on persuading people that independence is right for Scotland as he launched his campaign to be Nicola Sturgeon’s deputy.
Ms Sturgeon is preparing the ground for another independence referendum - but said she will only stage a re-run if she cannot find another viable option to keep Scotland in the European Union (EU).
Mr Robertson said he would use his position as SNP deputy leader to “deliver our goal of independence”.
He said: “We are on the brink of independence; the campaign that comes now should be all about persuading people why our vision is the right one for Scotland.
“The SNP depute leader has a big role in order to make this happen - developing our policy, strategy and tactics to win.
“I’ve spent the last year holding the UK Government to account every single week at PMQs.
“Alongside a team of extremely hard-working MPs, we’ve turned the SNP from the third party of the UK to the most effective opposition party.
“It is this kind of work ethic that will see us succeed in our mission and I know that I can work with Nicola to make it happen.
“From today, I’m also launching my bid to bring on board five thousand pledged supporters to my campaign before the nominations close.
“My vision for this role is about unity, campaigning and delivering our goal of independence.”
Mr Robertson’s most high-profile challenger is Alyn Smith, the MEP who received a standing ovation in Brussels for his plea to EU members to respect Scotland’s vote to remain.
Mr Smith has offered to be “a freelance roving sherpa” for Ms Sturgeon in Europe to get the best deal for Scotland.
Other contenders are MP Tommy Sheppard and councillor Christopher McEleny.
SNP membership has risen beyond 120,000 in the aftermath of the UK’s vote for Brexit, according to new party figures.
Membership now stands at 120,203 - growing by more than 4,000 since the Brexit vote and a fivefold increase from the 25,642 members on the day Scotland voted No to independence in September 2014.
SNP business convener Derek Mackay said: “The incredible upsurge in SNP membership shows no signs of stopping - with membership now over 120,000, putting the party in a strong position as we deliver our ambitious manifesto in government and lead the opposition to the Tories at Westminster.
“This extraordinary increase in membership makes clear that it is the SNP which people trust to stand up for Scotland’s best interests - in contrast to a Labour Party in complete disarray north and south of the border, and a Tory party which has taken Scotland to the brink of being dragged out of the EU.
“That membership has grown substantially since the EU referendum vote is testament to the strength of feeling in Scotland that we must not be dragged out Europe against our will - and the SNP in government will continue to explore every option to maintain our EU status.”