Williams joins the agency's board and will be responsible for its overall creative output, as well as working directly on key accounts such as Carling, SkyBet and Lloyds TSB Autolease.
Williams has more than 15 years of agency experience, including creative director and senior creative roles at Evans Hunt Scott, Liquorice, McCann Erickson and Lowe Howard Spink.
Williams said: "Mobious is becoming famous for stealing clients from under the noses of London agencies so I thought if you can't beat 'em why not. I'm delighted to be part of such an exciting agency at such an exciting time."
He was recently creative consultant to mobile gaming start-up Playonthego, and before that was founding partner and creative director of his own agency, Contact.
Iain Gibbons, joint managing director of Mobious, said: "Tom joins us with an enviable CV of producing award-winning creative and we are delighted to have him."
Mobious' former creative director Berry Burgess has left to set up his own design agency.
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