The move came as the marketing communications group revealed its annual results and announced plans to raise money for acquisitions.
Buhlmann, who takes over the role from interim chief executive and chairman John Napier on 1 May, will also retain his role as chief executive of Aegis Media.
Aegis had been without a group chief executive for a year-and-a-half since the departure of Robert Lerwill.
Buhlmann will be given increased financial flexibility and the potential for "bolt-on acquisitions" with the issue of a US$266 million convertible bond, according to the group’s annual results announcement.
Aegis reported a 22 per cent fall in its underlying pre-tax profits for 2009 and a 9.7 per cent drop in full-year organic revenue, but said it expected modest growth in 2010.
The group, which comprises Aegis Media and market research division Synovate, reported an operating profit of $258 million, full-year revenue of $2 billion, and a pre-tax profit of £226 million.
Aegis Media reported an operating profit of $228 million in 2009, a fall from the previous year's figure of $240 million.
Napier said: "We performed well to meet market guidance in a tougher year than we initially expected.
"We also strengthened our balance sheet and financial position, leaving Aegis well placed to meet the challenges of 2010, which we believe will bring modest growth."
Aegis spent $18 million on acquisitions last year after averaging $152 million per year for the previous five years.
Buhlmann stated that future acquisitions will be focused on developing markets such as China, as well as the US and Europe.
"We want to continue our strategy of 'buy and build' and our focus will be on developing markets", he said.
Napier and Buhlmann also ruled out any future tie-ups with Vincent Bollore, the chairman of rival Havas, who controls a 29.9 per cent stake in Aegis Media.
Buhlmann became Aegis Media global chief executive in May 2008, when he took over from Mainardo de Nardis. Prior to that, he was chief executive of Aegis Media EMEA for five years.
His previous positions also include a stint at Carat International as chief executive for three years, Young & Rubicam, WCRS and the media agency BBJ, which was bought by Aegis in 1999.