The Scottish first minister said the declaration was “a public promise” to act on global warming and had been inspired by young protesters who went on strike from school to urge action.
At least 90 councils across the UK have declared a climate emergency and pledged to work to limit damage to the environment.
MPs in Westminster will vote on whether to follow suit on Wednesday, after Labour forced a Commons debate on the issue following mass protests over political inaction on the crisis.
The declaration of a climate emergency is one of the key demands of environmental campaigners including the Extinction Rebellion movement, which paralysed parts of London with protests in the last fortnight.
Speaking at Scottish National Party’s (SNP) spring conference in Edinburgh on Sunday, Ms Sturgeon said: “A few weeks ago I met some of the young climate change campaigners who’ve gone on strike from school to raise awareness of their cause.
“They want governments around the world to declare a climate emergency. They say that’s what the science tells us, and they are right.
“Today, as first minister of Scotland, I am declaring that there is a climate emergency and Scotland will live up to our responsibility to tackle it.”
The UK’s Committee on Climate Change will this week publish a report which is expected to recommend more ambitious action to cut carbon emissions.
“If that advice says we can go further or go faster, we will do so,” Ms Sturgeon said. “Scotland will lead by example.
“I am making this public promise to the young people I met, and to their entire generation.”
Scotland's parliament has been repeatedly targeted by climate change protesters, including Extinction Rebellion.
Last month the SNP's MSPs joined other parties in voting against a Scottish Greens motion calling for parliament to declare a climate emergency.
Scottish Greens MSP Mark Ruskell, the party's climate spokesman, welcomed the SNP's "dramatic u-turn" on the issue but said "actions speak louder than words".
He added: “Declaring a climate emergency is about more than posing for pictures with climate strikers, it’s about ditching policies that are destroying the planet and investing in the jobs and technologies of tomorrow, today.”
There is no single definition of a "climate emergency" and a declaration in itself is not a commitment to specific action. However, many areas to have declared a climate emergency have said they will aim to be carbon-neutral by 2030.
The UK is currently committed to reducing greenhouse gas emissions by 80 per cent from 1990s levels by 2050. But campaigners and climate scientists warn this would not be enough to avert environmental catastrophe, with Extinction Rebellion demanding the UK government commit to zero carbon emissions by 2025.
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