Harriet is the illegitimate daughter of an unknown someone—the identity of her father is revealed later. He had placed her, years back, at Mrs. Goddard's boarding school.
Mrs. Goddard wanted to bring her to Hartfield estate for tea with Henry Woodhouse and his younger daughter, Emma. This was welcome, as Emma had always wanted to meet Harriet because of her beauty. She was excited, an also very nervous, to meet the Woodhouses, particularly Emma, who was such a well-known personage in Highbury. Her concerns were soon put to rest by how genial Emma was, and Harriet was especially happy that Miss Woodhouse had shaken hands with her.
Emma continued to invite Harriet to Hartfield, and thus succeeded in finding a new good friend to help her get over Mrs. Weston's departure. Emma was dismayed to discover that Harriet had developed feelings for Robert Martin, a farmer who lived near Donwell Abbey, as she thought the match and relation generally unsuitable.
She is described a being quite pretty, short, and plump, with a fine complexion, blue eyes, and blonde hair. She was well-mannered, and impressed Emma with her sweet-natured personality.
She is also unsophisticated and is too easily led by others, especially Emma. Emma takes Harriet under her wing early in the novel, and she becomes the subject of some of Emma's misguided matchmaking attempts. Harriet initially rebuffs a marriage proposal from farmer Robert Martin because of Emma's belief that he is beneath her, despite Harriet's own doubtful origins. She then develops a passion for Mr. Knightley, which is the catalyst for Emma realising her own feelings. Ultimately, Harriet and Mr. Martin are wed, despite Emma's initial meddling. The now wiser Emma approves of the match.