Speaking ahead of the SNP conference in Edinburgh next weekend, Keith Brown said the Tories and Labour were both failing to offer a positive vision to voters.
Mr Brown also claimed his party have often been the “only adults in the room” at Westminster during Brexit talks.
“The SNP head into this week’s conference on the back of increasing support and a determination to do everything we can to protect Scotland’s interests and present a positive, optimistic and outward-looking vision for Scotland,” said Mr Brown.
“Since 2016, across Westminster, the SNP have often been the only adults in the room, the only party focused on offering a serious sensible way forward out of the Brexit mess.
“The Scottish Tories have completely sold out Scotland’s interests over Brexit and are happy to let Westminster do whatever they want to Scotland.
“Meanwhile, Labour are quietly signing up to deliver a Tory Brexit - against the wishes of the people of Scotland - and without putting the issue back to the people.
“Labour and the Tories no longer have a positive vision to offer the people of Scotland. They are running scared of any debate over Scotland’s future - especially one that would see more decisions about Scotland taken in Scotland.
“In stark contrast, the SNP continues to win the support of people across the country, to listen to communities across the country and to set out a positive vision for Scotland’s future.”
A spokesman for Scottish Labour said: “This is a distraction from the real and serious problems Scotland faces - a low-pay economy, exhausted public services and one in four children living in poverty.
“Labour has a plan worth £70 billion of investment in Scotland, with more democratic control of our economy and improving public services.
“Meanwhile, the SNP don’t know what currency Scotland would use outside the UK and have no answer to the unprecedented austerity it would bring.”
Scottish Conservative chief whip Maurice Golden said: “It speaks volumes that the SNP only want to talk about independence on a day when we learn that the number of Scottish pupils leaving school without a qualification is on the rise.
“Most people want to move on from endless debates on the constitution, but the SNP just won’t let it go.
“Scotland faces years more of the SNP putting its obsession with independence above all else. Instead, we can have a fresh government led by Ruth Davidson, getting on with making Scotland a better place for everyone.”