Fleming takes on the role of UK head of corporate communications and marketing, with a remit to build the firm's profile in the UK media, boost the in-house PR team and design a pro-active PR plan.
Founded in the US more than 130 years ago, Shearman & Sterling has until now concentrated the bulk of its PR efforts in the US, leaving just a single PRO covering the UK.
Fleming's appointment marks a turn-around in the firm's approach to UK comms.
'They've always considered themselves as a profession rather than a business and weren't marketing themselves,' said Fleming.
'They've never had anybody doing real proactive PR (in the UK) before, but now they believe the competition is expanding, they're developing and want to get the name out there,' he added.
Shearman & Sterling currently employs a UK PR team of two, including Fleming, who aims to boost this to eight within two years.
At Andersen, Fleming was senior comms manager for the European corporate finance division, prior to which he worked as an account director within Edelman PR Worldwide's financial practice.