The Scottish First Minister said that in an "ever-changing world, especially in turbulent times" the Queen had been a "great constant".
She also spoke about the Queen’s "genuine love of Scotland" and her "profound sense of public service", which Ms Sturgeon said "never faltered".
Her comments came ahead of tributes to Elizabeth II at a special sitting of the Scottish Parliament later on Monday.
All business there was suspended last week after it was announced on Thursday that she had died peacefully at Balmoral Castle.
King Charles III will be in Holyrood with his wife, the Queen Consort, to hear tributes from Ms Sturgeon and the other party leaders in the Motion of Condolence – which is taking place after a service of prayer and reflection for the life of the Queen at the nearby St Giles’ Cathedral.
The Queen’s body will lie in rest at St Giles’ after that service, with thousands of Scots expected to go there to pay their final respects.
Crowds are already gathering in Edinburgh at what Ms Sturgeon said was a "moment of profound sadness" for countless numbers of people both in the UK and across the world.
The First Minister stated: "This Parliament and this nation are in mourning today.
"At the heart of it all, of course, is the sense of loss felt by those who were closest to Her Majesty.
"Our thoughts are with the entire royal family – and we are honoured by the presence here, of His Majesty, King Charles III, and The Queen Consort."
Ms Sturgeon continued: "In an ever-changing world, especially in turbulent times, Her Majesty was the great constant – the anchor of our nation.
"Even towards the end, as her health declined, her genuine love of Scotland and profound sense of public service never faltered.
"She performed her duties with dedication and wisdom, setting an exceptional example to each and every one of us.
"We stand ready to support His Majesty as he continues his own life of service and builds on the extraordinary legacy of his beloved mother Queen Elizabeth – the Queen of Scots."
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