Start Creative will also help to manage email and newsletter campaigns for the brand.
Narisa Najurally, user experience lead at UpMyStreet, said: "Start understands our business well, and manages expectations from a consumer and supplier perspective with its design solutions. It is our agency of choice and we intend to build a long-lasting relationship."
The agency plans to retain the brand's independence from uSwitch, but will look to link the two where possible. USwitch enables users to switch utility suppliers, such as gas, as well as banking services.
Stuart Ledden, new media account director at Start, said: "We have only just started the project, but we'll look to apply the learnings we already have. They are very different propositions, but we'll be looking at ways to cross-fertilise."
Start began working with uSwitch in 2002, initially making the firm's site easier to use. It has since helped in the design of new pages, such as the banking section. The new site is due to launch at the start of 2005.
USwitch bought UpMyStreet when the service entered administration in April 2003 after failing to find new funding.