Bunten was previously a board director at the agency, which she has worked for since it was launched in 2004. She will continue to oversee its global account for pharmaceutical giant Novartis.
Tierney has joined in the new role of deputy managing director after four years as a director at Just Health, which is understood to have lined up a replacement.
Tonic Life group CEO Scott Clark said: "As Tonic continues to grow with our clients, these appointments will help maintain our momentum and strengthen the depth of our leadership team."
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