In the customary ceremony at the highest court in Scotland, Mr Yousaf pledged his allegiance to the King, as well as to serve him in the role as First Minister and Keeper of the Seal of Scotland.
His family watched on from the public gallery, and he was flanked by Lord Advocate Dorothy Bain KC.
Mr Yousaf will spend the rest of Wednesday appointing his Cabinet, with his chosen ministers set to visit his official residence at Bute House throughout the day before an announcement later in the afternoon.
9. Humza Yousaf is sworn in as First Minister of Scotland
The oath was administered by Lord Carloway, the Lord President, who heads up the judiciary in Scotland. Photo: Jane Barlow
10. Humza Yousaf speaks with members of the public outside the Court of Session in Edinburgh
Humza Yousaf speaks with members of the public outside the Court of Session in Edinburgh after being sworn in as First Minister of Scotland. Photo: Jane Barlow
11. Humza Yousaf, with his family arriving at Bute House
Humza Yousaf, with his wife Nadia El-Nakla, daughter Amal, three, and step-daughter Maya (left) arriving at Bute House, Edinburgh Photo: Andrew Milligan
12. Humza Yousaf at Bute House
Humza Yousaf at Bute House, Edinburgh, ahead of his first cabinet meeting as the newly elected First Minster of Scotland Photo: Andrew Milligan