The agency, founded by the former chief executive of Proximity London Amanda Phillips and former Partners Andrews Aldridge managing partner Chris Ward in February, won the account following a competitive pitch.
Big Al's Creative Emporium previously handled the account.
An Abundance will be responsible for developing creative campaigns across the H&T Group product and service lines including pawnbroking, gold purchasing, unsecured loans and retail jewellery.
Lucy Westcott, head of marketing said: "Our customer loyalty is high and we are exceptionally proud of the brand work we have done.
"It's a complex sector with many dynamics but An Abundance totally understood it and their pitch was superb. They delivered a strategic platform that was both right for the sector right now and us as the dominant player in that sector."
Chris Ward, co-owner and managing partner An Abudance said: "H&T's proposition and offering to all socio demographic groups is compelling. Arguably we are doing the easy bit by building on years of investment in a culture and service proposition that has got them to number one in the market."
H&T was established in 1897 and is the oldest and biggest player in the pawnbroking and cash for gold sector, according to the company.
An Abundance's other clients include Royal Mail, Barnardos and Unilever.