Geoghegan, who has been with the agency since 2005, replaces former MD Gavin Davis, who tendered his resignation in September to join Sky.
She will take up the role as of 1 January and will report to division chairman John Sunnucks, who said her "close client relationships, professional handling of complex issues, and strong leadership skills" make her the right person for the job.
Group CEO James Henderson added: "Victoria's energy, commitment and broad range of skills embody what we want as we reset and look to our next phase of growth."
This year has seen various senior personnel changes at Bell Pottinger, with agency founder Lord Bell resigning as chairman in August to focus on his new PR business called Sans Frontières.
Earlier, head of creative engagement Kev O'Sullivan left Bell Pottinger after seven months in the role, to join FleishmanHillard Fishburn.
