Shah is due to start at Black Tomato on 16 December, after he left DBMT in October amid a number of redundancies following a restructure at the agency.
In his new role, Shah will oversee the agency's existing BMW account, as well as a number of new clients.
Shah said: "I had a great time at DBMT and gained a lot of experience. I was offered another role when the agency restructured, but it wasn't the right move for me.
"I proactively contacted Black Tomato because it is an agency that's impressed me in the past. I think it brings a lot to the market and the brands it works with, and I'm really pleased to be joining next week."
Shah joined DBMT in January 2012 as an account director, heading up the travel and events team. He started in the industry at Motivaction Group in 1998 before joining Grass Roots, where he spent 11 years.
Elliott Grant, business development director of The Black Tomato Agency, said: "Chetan has more than 15 years' experience in the events industry, particularly in the automotive sector. He will help to develop our relationships with existing clients, including the BMW Group, and develop our presence in the automotive sector.
"Our core markets are automotive, IT and direct selling, and we now have a solid team in place to grow our presence in these areas in 2014. A new marketing manager has been appointed from within and so we will have a renewed marketing focus next year."