Lewis' career has spanned both the private and public sectors. He joins FTI from the Association for Financial Markets in Europe (AFME), which he founded to be the voice of Europe's wholesale financial markets. He was chief executive there for nine years.
Lewis was previously director of comms and official spokesman for Prime Minister Gordon Brown, and was the Queen's first communications secretary. He has also held senior corporate roles, including director of corporate affairs at Vodafone, Centrica and NatWest.
In his role as vice-chairman, Lewis will help develop FTI's client relationships across the region and support the firm's strategic initiatives. As global head of financial services, he will work closely with senior leaders throughout the firm to maximise business success in this sector.
He said: "At a time of political and economic flux, there is a greater demand than ever from clients for a combination of public- and private-sector experience."
Lewis will assume his new roles in January.
Mark McCall, global segment leader of the strategic communications segment at FTI said: "Amid the backdrop of continued commercial uncertainty, Simon's diverse experience will further strengthen our ability to help financial services clients advance and protect their reputations, engage with stakeholders, manage change and mitigate risk."
"Simon will be an excellent addition to our regional team," added Kevin Hewitt, FTI chairman of the EMEA region.