The 29-year-old becomes the youngest ever MSP and first ever woman to hold the role.
The former finance secretary has been dropped from his role as an honorary vice-president.
From income tax to benefits changes, what do the government's spending plans mean for your pocket?
Minister Kate Forbes revealed a raft of measures 'to accelerate the transition to a net-zero economy'.
Mackay has quit after allegedly sending hundreds of messages to a 16-year-old boy.
Derek Mackay will publish his draft spending plans on February 6, prior to the UK Budget on March 11.
The number of private sector businesses operating in the country has risen by more than a quarter since 2007.
Finance secretary Derek Mackay blamed 'disastrous' mismanagement by recently nationalised firm Ferguson Marine.
The latest economic figures show Scotland has returned to growth, with GDP rising by 0.3% in the last quarter.