Xerox Corp.’s deal to sell a majority of itself to Fujifilm Holdings Corp. was temporarily blocked Friday night by a judge who said the transaction was negotiated by a “massively conflicted” chief executive who was looking out for his own interests over Xerox shareholders’.

In an opinion following two days of hearings for a lawsuit brought by one of Xerox’s biggest investors, the judge slammed Xerox CEO Jeff Jacobson and the company’s board for approving the deal, calling their arguments “counter-intuitive and not credible.”...