Proximity, which handles direct marketing for Mars' Dolmio and Uncle Ben's brands, secured the business without a pitch.
The agency will take responsibility for all ad communications, including TV, press and posters. Seeds of Change currently sponsors Channel 4's food programme Willie's Wonky Chocolate Factory.
The idents reflect the brand's new identity, which was created in February by the design agency Dragon in a bid to attract a younger demographic of consumer.
Mars, owned by Masterfoods, hired TBWA to handle the Seeds of Change account following the agency's resignation of the Cadbury business in 2002.
TBWA went on to secure other Masterfoods brands, including Whiskas, Skittles, Lockets and Tunes.
The agency has produced a number of press ads for the organic food brand, plus a poster campaign for Seeds of Change cooking sauces.
The ads aimed to shun the hippy stereotypes usually associated with organic food by using lines such as: "Keep those free love shenanigans away from our extra virgin olive oil."