Gossage told his wife's best friend the Harry Potter scribe penned the novel under the name of
Robert Galbraith and the woman spilled the secret to a journalist via Twitter last summer.
In addition to the fine, the SRA also issued a written rebuke to Gossage, a partner at Russells Solicitors, for breaching privacy regulations, the BBC said.
Rowling accepted the law firm's apology and was paid undisclosed damages, which she donated to charity.
2014: The Year in Fashion [PHOTOS]