And an independent Scotland would not adopt the euro if it rejoins the EU, Mr Mackay insisted - despite this being Brussels policy for new member states.
The Finance Secretary said he hoped SNP delegates would back a motion at next month's party conference to change policy and commit to a new Scottish currency following independence after using the pound for a transition period.
The party's recent Sustainable growth Commission, which Mr Mackay sat on, proposed that the new currency would only be adopted after the £13 billion deficit - the gap between public spending and taxes raised to fund them - is halved. It estimated this could take 5-10 years.
Asked today, if this could be done sooner, Mr Mackay told BBC Sunday Politics Scotland: "Yes and I can tell you why.
"After we published the growth commission report our economics and the financial position was improving.
"With the powers of independence , yes we can stimulate economic growth, grow our economy, get that notional deficit down."
And insisted that it would not mean years of austerity.
"We've got austerity in Scotland and in the UK because it was the choice of the Conservatives - it was a political choice and it's no longer a necessity," he added.
"We can grow our economy, we can grow our public services, we can grow out GDP faster than being part of the UK that subduing and now endangering our economy. "
New EU members states must commit to joining the EU, but the SNP points to Sweden which has yet to adopt the single currency after 25 years in the EU.
"It's not compulsory to join the euro," Mr Mackay added.
"We're proposing continuing with the pound, so that's continuation of pound sterling and we have the ambition to have an independent Scottish currency and set out a plan to take us there.
But pro-union opponents insisted that the SNP's plans would be a "recipe for deeper and tougher austerity."
Pamela Nash, chief executive of Scotland in Union, added: “Derek Mackay’s support for ditching the pound and introducing a new currency is the height of irresponsibility, and even he has been forced to admit it would be high-risk.
“He is all over the place, also astoundingly ignoring that new member states in the EU must commit to joining the euro."