In the first film, Grimsby is shown sailing with Eric and his crew, apparently suffering from seasickness. He overhears the crew talking about mermaids and dismisses the talk as nonsense, advising Eric to do the same. They, however, insist that merpeople really exist.
Later in the film, the crew is celebrating Eric's birthday on board the ship. As a birthday present, Grimsby presents Eric with a large statue of him, 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. He responds that he will marry when he finds the right girl.
Later, the ship is caught in a storm, with Grimsby, Eric, and the crew all thrown overboard when the ship crashes into a gaggle of rocks. Grimsby and the crew are able to reach a lifeboat, but Eric returns to the ship to save his dog, Max, who is still trapped on board. Max is able to safely get to the lifeboat, but the ship explodes due to fire that reaches into the barrel of gunpowder, and Eric is thrown overboard. Grimsby later finds Eric safely on shore, where he reveals that a girl (actually Ariel, unknown to either) saved his life and sang with her beautiful voice. Grimsby dismisses Eric's claims as a result of him 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 by Ursula, Grimsby notes that she is beautiful. Later Eric finds her and brings her to his palace and to where she is invited to dinner and Grimsby tells his boss that nice young ladies like Ariel don't go around rescuing people or disappearing, to which Eric disagrees and vows to marry the girl with the lovely voice. Ariel takes Grimsby's pipe (thinking it will play music, and remembering Scuttle's poetic description) and blows its contents into his face. He says that Eric should take her on a tour of the kingdom to which he agrees and does so. As time goes on, Grimsby notices that Eric is falling for Ariel. He councils him to forget his dream girl (he wished to marry the one 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 it, Scuttle and other birds and sea creatures swarm in and stop it, which causes Vanessa's spell to break and Ariel's voice to return to her. Ursula resumes her normal form and kidnaps Ariel. Eric follows them in a rowboat, causing Grimsby to question his actions. In the end, after Ursula is destroyed and Ariel is turned into a human, she and Eric 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 him and asks him if their prior actions towards Ursula were fair. He is later present at Melody's twelfth birthday party, where he formally presents her as she enters. He later watches sadly as she runs away from there.
Grimsby is not seen again until the end of the film. As everyone is celebrating in the water, Eric asks him to come in and join them. He 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 of 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 in One Hundred and One Dalmatians. Coincidentally, Grimsby has a similar nose and smokes a pipe, just like Roger.
- Grimsby was Ben Wright's final film role; he died before The Little Mermaid was released.
- In the Broadway show, Grimsby was portrayed by Jonathan Freeman, who is more famously known for voicing Jafar of Aladdin.