Their appointment follows a period of growth for the agency, which was set up three years ago by the St Luke's founding creative directors, Naresh Ramchandani and Dave Buonaguidi.
The agency picked up the Emap Performance creative brief last year and has turned its initially project-based clients UKTV, Ikea and VH-1 into retained accounts.
"We took Matt and Vic on because we were impressed with the way that they don't wait for opportunities - they go out and grab them," Ramchandani said. "They have a lot of initiative as well as creative talent."
The pair, who both art direct and write, first became a team at St Luke's three years ago. They join after only three months at Lowe, where they began working on HSBC, Diet Coke and Olympus. Polkinhorne said: "Karmarama has got big plans and so have we. It's looking to attract new pieces of business and we enjoy doing lots of work but, more than that, the style of the company and the people here just suited us."
While at St Luke's, they created Travelocity's "stopover" ad, which was the runner-up in February's Aerial Awards and which will be entered for this year's D&AD.