Brown, who joins Apella as a partner, is a senior corporate affairs executive who has worked across the insurance, energy, business services and telecoms sectors.
He joins from Ageas Insurance, where he was director of communications and public affairs. He has also served as a comms director at renewable energy giant Drax Group and global corporate affairs director at Regus (now IWG).
Miller, who joins as a director, has more than a decade of experience in corporate positioning and reputation management. Prior to Apella, he was associate director at APCO Worldwide, and has also spent three years at Grayling.
He has worked with clients including Lockheed Martin, Naftogaz, Enviva and TVO.
Apella Advisors, which was formed in April by founding partners James Acheson-Gray, Jenny Scott and Matt Young, with Anthony Silverman joining in May, has further senior hires planned for the coming months.
"Andrew and Doug between them have a powerful combination of operational experience within organisations, as well as records of effective reputation management – which we can deploy within our growing client roster," Young said. "They are significant additions to the Apella team."