What was James Potter's job? [duplicate]

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• Where did Harry's parents get all of their money from? 8 answers

At the start of Harry Potter and the Prisoner of Azkaban Aunt Marge and Uncle Vernon have following conversation:

“This Potter,” said Aunt Marge loudly, seizing the brandy bottle and splashing more into her glass and over the tablecloth, “you never told me what he did?”

Uncle Vernon and Aunt Petunia were looking extremely tense. Dudley had even looked up from his pie to gape at his parents.

“He — didn’t work,” said Uncle Vernon, with half a glance at Harry. “Unemployed.”

Was he really? Is there any canon source about what he did for living besides this one?

I also find but it is quite possible that Vernon is not telling the truth in this case (or has no idea).