In the first movie, Grimsby is shown sailing with Prince Eric and his crew, apparently suffering from seasickness. He overhears the sailors talking about mermaids and dismisses the talk as nonsense, advising Eric to do the same. The sailors, however, insist that merpeople really exist.
Later in the film, the crew is celebrating Eric's birthday on board the ship. As a birthday gift, Grimsby presents Eric with a large statue of the prince, though Grimsby remarks that he wished it could have been a wedding present. The film reveals that Eric recently refused to marry a princess from another land. Grimsby remarks that the entire kingdom, himself included, wishes to see Eric happily married. Eric responds that he will marry when he finds the right girl.
Later, the ship is caught in a hurricane, with Grimsby, Eric, and the crew all thrown overboard. Grimsby and the others are able to reach a lifeboat, but Eric returns to the ship to save his dog Max. Max is able to safely get to the lifeboat, but the ship explodes due to fire, and Eric is thrown overboard. Grimsby later finds Eric safely on shore, where Eric reveals that a girl (actually the mermaid Ariel, unknown to either) saved his life. Grimsby dismisses Eric's claims as a result of Eric swallowing too much seawater, and returns to the palace with Eric and Max.
When Eric discovers a mute Ariel, who had been recently transformed into a human, Grimsby notes that the girl is beautiful. Later Eric finds Ariel and brings her to his palace and to where she is invited to dinner and Grimsby voices his opinion that she is beautiful. Ariel takes Grimsby's pipe and blows it (thinking it will play music) and she blows its contents into his face. Grimsby says that Eric should take Ariel on a tour of the kingdom to which Eric agrees and does so. As time goes on, Grimsby notices that Eric is falling for Ariel. He councils Eric to forget his dream girl (Eric wished to marry the girl who saved him, not realizing it was Ariel), and to accept the real one he has.
Later, Ursula, disguised as Vanessa, arrives and uses Ariel's voice to enchant Eric into marrying her. Grimsby is surprised at this turn of events, but agrees to arrange for a wedding at sea. During the wedding, Scuttle and other birds and sea creatures swarm in and stop the wedding, which causes Vanessa's spell to break and Ariel's voice to return. Ursula resumes her normal form and kidnaps Ariel. Eric follows them in a rowboat, causing Grimsby to question Eric's actions. In the end, after Ursula is destroyed and Ariel is turned into human, Eric and Ariel are married. At the wedding, Carlotta grabs Grimsby's shirt and cries happily in it.
Grimsby returns in the sequel but, has a smaller role than in the previous film. He is present at the celebration of Melody's birth. When Ursula's sister Morgana arrives, she grabs Grimsby and asks him if their prior actions towards Ursula were fair. Grimsby is later present at Melody's twelfth birthday party, where he formally presents Melody as she enters. He later watches sadly as Melody runs away from the party.
Grimsby is not seen again until the end of the film. As everyone is celebrating in the water, Eric asks Grimsby to come in and join them. Grimsby attempts to refuse, but before he can finish, he is knocked into the water by Max.
- Grimsby shares the same voice actor as Roger Radcliffe of One Hundred and One Dalmatians and Rama in The Jungle Book. While Ben Wright was auditioning for Grimsby, the producers didn't know who he was so he had to end up telling them he provided the voice of Roger for One Hundred and One Dalmatians. Coincidentally, Grimsby has a similar nose and smokes out of a pipe, just like Roger.
- Sadly, Ben Wright, the voice of Grim, died just before The Little Mermaid came out.
- In the Broadway show, Grimsby was portrayed by Jonathan Freeman, who is more famously known for voicing the classic villain, Jafar.