Buchanan fought off competition believed to include Brunswick, Tulchan, FTI Consulting, Pelham Bell Pottinger and MHP to pick up the ex-M:Communications client.
Cape, listed on the main market of the London Stock Exchange, provides fire protection and scaffolding to the energy and natural resources sector.
The account team at Buchanan is led by Bobby Morse, who commented: 'Cape is an outstanding business. The new management team at Cape have an exciting opportunity to generate significant returns for shareholders.'
Joe Oatley was installed as Cape's chief executive in June last year after a series of profit warnings saw the firm's valuation tumble by two-thirds.
