By Michael Holden and Sam Tobin

LONDON, Dec 15 (Reuters) - Britain's Prince Harry will learn on Friday whether he has won his lawsuit against a newspaper publisher over allegations of phone-hacking and other unlawful acts, the biggest ruling so far in his legal war against the British tabloid press.

The prince – who became the first senior British royal for 130 years to give evidence in court when he appeared as the star witness at the trial in June – is suing MGN, the publisher of the Daily Mirror, Sunday Mirror and Sunday People.

Harry and about 100 other claimants – which include actors, sports stars, celebrities and people who simply had a connection to high-profile figures – are taking legal action over allegations of phone-hacking and unlawful information-gathering between 1991 and 2011.

They say senior editors and executives at MGN knew about and approved of the wrongdoing. MGN, owned by Reach, says their accusations are not supported by the evidence.

Judge Timothy Fancourt will deliver his ruling at London's High Court at 1030 GMT.

Harry, King Charles' younger son and the fifth in line to the throne, was selected as one of four test cases for the trial. Over two days of giving evidence, he said he was targeted by MGN for 15 years starting in 1996, and is seeking damages of about 440,000 pounds ($550,000).

"I would feel some injustice," he said when asked how he would feel if the court concluded he had not been a victim of phone-hacking.

While the publisher admitted that Harry had on one occasion been the victim of unlawful information-gathering, to which it said he was entitled to no more than 500 pounds in damages, its lawyer said there was no evidence that the prince's phone had been hacked at all.

Since stepping down from royal duties in 2020 and moving to California with his American wife Meghan, the Duke of Sussex has made it his mission to rid the British press of those he accuses of being "criminals masquerading as journalists", especially senior executives and editors.

So far he has had mixed fortunes.

He won the right to take to trial a similar phone-hacking case against Associated Newspapers, the publisher of the Daily Mail and Mail on Sunday, which he has brought with high-profile figures including singer Elton John.

But earlier this week, he lost a bid to win a libel claim against the same publisher without the need for a trial, at a cost in legal fees of at least 50,000 pounds.

His allegations of unlawful behaviour by News Corp's News Group Newspapers, the publisher of the Sun, will also go to trial, but the judge rejected his bid to have claims of phone-hacking considered.

(Writing by Michael Holden; editing by Mark Heinrich)