McCall had previously served on Perth and Kinross Council, and stood for the Dunfermline seat at the previous election.
Lockhart, who had served as an MSP since 2016, was the convener of Holyrood’s Net Zero, Energy and Transport Committee.
Ms McCall said: “I am delighted and honoured to join the Scottish Conservative MSPs in Holyrood.
“As an MSP I will work to reverse the erosion of local democracy, to hold the SNP government to account, and to provide alternative, new and imaginative, positive policies to benefit the people of Mid Scotland and Fife, and Scotland as a whole.”
Dean Lockhart said: “It has been an absolute privilege to represent the people and region of Mid Scotland and Fife over the past six years.
“Given the vital importance of addressing climate change and delivering on net zero targets, I have decided to accept an offer to join a business organisation that works together with governments, local authorities and third sector bodies, and that will help finance and deliver Net Zero targets across the UK.
“I would also like to express my sincere thanks to Douglas Ross for his outstanding leadership and support, and to wish him and all my colleagues all the very best for the future.”
Scottish Conservative Leader Douglas Ross said: “I would like to thank Dean for his sterling work in the parliament, and wish him well in his new venture, where he will continue his work in tackling the challenges of climate change.
“I look forward to working with Roz, who will now continue her long-standing efforts to deliver real improvements in people’s daily lives from Holyrood.
“Like the rest of the Scottish Conservative group, she will work tirelessly to hold this SNP administration to account and focus on the real priorities of Scotland’s people.”
The appointment follows the usual procedure when a list MSP steps down.