John Charman's attempt to oppose an interlocatory injunction, filed by former employer Ace, has been thrown out by the High Court in London.
Ace filed an injunction on 1 October. It was discovered that Charman had been appointed chief executive of Bermudan start-up insurer Axis Specialty at the end of September.
Charman left Ace International, where he was group president and chief executive, on 17 March after "differences over personal matters".
Charman was being paid for a year's gardening leave after being dismissed by Ace. But last month, Insurance Times revealed Ace had launched an interim injunction to prevent him from taking up further employment during that time.
Charman, who received £82m worth of shares when Ace bought his underwriting agency for £349m in July 1998, had been appointed as chief executive officer and run-off director of Lloyd's insurer Newmarket.
He has also joined Axis Specialty, Marsh & McLennan's new $1bn (£680.4m) insurance and reinsurance operation, as chief executive and is expected to invest $20m (£13.9m) into the Bermudan start-up.
Ace International's lawyers Allen & Overy confirmed the Royal Court of Justice had now rejected his attempt to oppose the injunction and that the matter would proceed to a trial scheduled on 26 November to determine whether he was in breach of contract.
Justice Jeremy Cooke ruled: "The common link of Newmarket and Axis to Marsh, when combined with the involvement of Mr Charman and his ex-employees with non-competitive Newmarket in London, and Mr Charman's involvement with competitive Axis in Bermuda, gives rise, the claimants can say, to strong suspicion.
"When the number of ex-employees who have left Ace for destinations unknown in the last few months since Mr Charman's dismissal is also taken into account... the claimants have, they say, good grounds to fear there will be breaches of soliciting ex-employees by Mr Charman. The refusals of Mr Charman to give undertakings in the past has enhanced these suspicions."