The North East Scotland MSP takes on the role after Mr Carlaw stepped up to interim leader following the resignation of Ruth Davidson last week.
Ms Davidson, who will remain at Holyrood as an MSP, has been appointed to serve on the Scottish Parliament's Corporate Body (SPCB) for the party - a position held previously by Mr Carlaw.
The only other change to the Tory frontbench team is Peter Chapman becoming the party's spokesman for the rural economy.
Mr Carlaw said: "Ruth's departure of course necessitated some immediate changes.
"But it also presents an opportunity to bring forward generation Ruth - people who were persuaded to get into politics because of her leadership.
"This move demonstrates the breadth of talent and experience within the Scottish Conservative team.
"Now the focus of not just the shadow Cabinet but the whole Scottish Conservative group will be to continue to hold the SNP to account in Holyrood, and fight tooth and nail for Scotland's place in the UK."