The agency, chosen without a competitive review, is responsible for strategy, branding, creative, website, digital and public relations.
Baker & Bonner will launch a new creative campaign in early summer.
Harry Smith, president-CEO of Pegasus Bank, said: "We were looking for an agency that could help us continue to build and evolve the brand. Baker & Bonner bring more than 50 years combined experience in branding and creative excellence."
Pegasus Bank is a full-service bank with three locations in Dallas and and $1.4 billion in assets.
Baker & Bonner's client list includes Community Coffee, Luckenbach Texas, London-based Jan Erika Design, Peacock Alley and Ranger Creek Brewing and Distillery.