Lewis (pictured) has advised global asset managers, pension consulting firms and alternative investors during a career that began at M&G Investments, followed by eight years at international communications consultancy CNC (now Kekst CNC).
Recently, she led corporate communications at FE, the fund industry data provider.
Lewis said: "The culture at Montfort is a breath of fresh air with great emphasis on senior advice and delivering for clients."
Gay Collins, founding partner at Montfort, said: "Claire is an outstanding hire and will help us maintain a rate of growth that has put Montfort into the very top bracket of communications advisers in the sector."
Montfort has doubled in size over the past year following a string of new business wins across all sectors.