The accountancy firm has spent more than £700,000 across the sites to bring its total property footprint in the city to around 15,000 square feet which it says "reflects the firm's confidence in the city's economic growth, across all sectors".
The Carden Place office houses Johnston Carmichael Wealth and the personal tax team, focusing on high net worth individuals.
Meanwhile, the newly reconfigured Albyn Place premises house the corporate teams, including tax, audit, corporate finance and business solutions.
Johnston, business of the year at the Scottish Accountancy & Finance Awards 2014, has also hired Mark Watson as a director in the tax team. Mr Watson was formerly leader of the tax practice at PricewaterhouseCoopers in Guernsey.
Niall Farquharson, joint managing partner of the Aberdeen office, said: "The past 12 months has seen a significant number of new clients which is an impressive reflection of the confidence Aberdeen's thriving business community has in Johnston Carmichael."
He added: "The investment has been made to provide our staff with a modern, fit for purpose working environment."