Walter Baker, the owner of the chocolate company and half-brother of Pierce's mother, hired him at a salary of three dollars per week.

At the request of Sydney Williams, brother-in-law of Baker and managing director of the chocolate mill, Pierce returned to Boston after a year and was appointed manager of the Walter Baker Counting House at 32 South Market Street in Boston (now a part of the Quincy Market retail area).

In 1856 the trustees extended the lease a further eight years, during which time Pierce began an expansion that would eventually absorb his competitors in the Lower Mills.

Walter Baker Chocolate never suffered from any labor movements under Pierce's ownership, and he was regarded as a kind and well-paying employer.

Pierce was elected as a Republican to the Forty-third Congress to fill the vacancy caused by the death of William Whiting.

He successfully had a commission revise the city charter and opened the Boston Public Library on Sundays[1][2] It was during his terms as mayor that Pierce's business began an extensive marketing and public relations campaign to make Walter Baker & Company a household name or, better, the household choice for chocolate and cocoa.

Used earlier in the company's history, this famous design was copied from the pastel portrait of Das Schokoladenmädchen by Jean-Étienne Liotard, an 18th-century Swiss painter.

He employed women to dress as the trademark come to life in silk gowns, with crisply starched white lawn aprons, caps and cuffs.

The article went on to say that at this food show, "one of the most noticeable exhibits of this sort is made by Walter Baker & Co., who occupy a conspicuous place just opposite the main entrance to the amphitheatre.

All are dressed in the costume of 'La Belle Chocolatiere' of Liotard's painting in the Dresden Gallery, made familiar to everybody as the trademark of this old established firm.

The soft draperies of the canopy are a pleasing frame for the quaint costumes and brilliant complexions of the chocolate girls, and even rival exhibitors praise the taste shown by the firm in displaying its wares so attractively."

These comely demonstrators, who elicited the praise of even the rival exhibitors at an exhibition, were only one aspect of Henry Lillie Pierce's astute ability to attract attention to his products.

In her book Crowding Memories, Mrs. Thomas Bailey Aldrich, widow of the former editor of the Atlantic Monthly, wrote of Pierce as a close friend to her and her husband.

Pierce's "deep and unaffected friendship" for the Aldriches was sincere, and they, like many others, benefited from his estate, inheriting his farm at Ponkapoag in Canton, Massachusetts.