The group said the reduction will take effect on 29 March and will save household gas customers on average £32 a year.
It follows just a week after rival E.ON announced it was lowering gas prices by 5.1% from 1 February.
The cut was praised by secretary of state for energy and climate change Amber Rudd as a "step in the right direction."
SSE's price cut will not take effect until after Easter, but SSE said it comes three months before its current price freeze comes to an end.
The group pledged to keep energy prices on hold in March 2014 until the end of June 2016.
Rudd called for other UK providers to drop their prices.
She said: "I'm absolutely clear that the market must provide a fair deal for consumers and that's why I've been pressing energy companies to put their customers first and pass on savings to them.
"SSE has taken a step in the right direction and I urge other suppliers to follow suit."
SSE insisted wholesale energy prices make up an "ever smaller proportion" of customer bills, with many other cost pressures affecting tariffs and limiting the ability to pass on cuts.
The group revealed it lost customers since last March, with electricity and gas accounts reducing by 30,000 to 8.28 million.
It said customers also used less electricity, down 3%, while gas usage remained flat.
Alistair Phillips-Davies, chief executive of SSE, said market conditions were "challenging", with the group hit by one of the warmest winters on record and the impact of Storm Frank on its networks in the north of Scotland last month, which saw winds of 90mph and significant flooding.
The group said it restored power to 93% of affected customers within 12 hours.
Phillips-Davies added: "I am pleased that we have been able to announce a reduction in retail gas prices - our third consecutive reduction in household energy prices - and to achieve a significant reduction in the number and duration of power cuts experienced by our network customers."
Dermot Nolan, chief executive of energy watchdog Ofgem, said: "This is a move in the right direction, but, if the market is as competitive as suppliers claim, we would expect to see further price cuts.
"Ofgem referred the market to the Competition and Markets Authority because we feel competition is not bearing down fast or hard enough on consumers' bills."