The appointment was made at a meeting earlier today in the presence of Her Majesty.
Ms Johnstone is now the sixth Presiding Officer of the Scottish Parliament to carry the title of Right Honourable.
The Rt Hon Elin Jones MA, Llywydd of the Senedd, was admitted at the same meeting.
The Presiding Officer, Rt Hon Alison Johnstone said:
“It was a great privilege to be elected Presiding Officer of the Scottish Parliament last May, and it was an honour to be made a Privy Counsellor by Her Majesty The Queen this afternoon.
“This appointment is recognition of the important role the Scottish Parliament and the Office of Presiding Officer plays and I am pleased to accept it.”