The Duke of Sussex was "singled out for different, unjustified and inferior treatment" in a decision to downgrade the level of security he receives in the UK, the Court of Appeal has heard.
Prince Harry is making his latest legal challenge after the High Court upheld the decision that he should not be provided with the same level of police protection given to working members of the Royal Family.
His barrister Shaheed Fatima KC told the court Prince Harry had been subject to a "different and so-called bespoke process" in that original decision.
The duke's security in the UK is currently decided on a case-by-case basis, the same way as the country's other high-profile visitors.
Prince Harry sat on Tuesday with a notepad and pen in the back row of the court, next to his solicitor and behind his barristers.
He did not give evidence in the first part of the hearing, which is scheduled to last two days.
The prince's case is challenging the way the Royal and VIP Executive Committee, known as Ravec, took the decision on his security arrangements after he stepped down from being a working royal in 2020.
He has previously said that the safety of his family, with whom he moved to California in 2020, was at the heart of the case.
"The UK is central to the heritage of my children," he told the High Court in December 2023, adding that he wanted them to feel at home here.
"That cannot happen if it's not possible to keep them safe."
Because the Home Office has legal responsibility for Ravec's decisions, it is opposing the appeal on its behalf.
Ms Fatima told the court on Tuesday that Ravec had not followed its own standard procedures, because it chose to downgrade his security without having expert analysis of the risks he faced.
She argued that the previous judge was wrong to have concluded that the committee could make decisions without such analysis.
She also said the prince's case was not that he should "automatically be entitled to the same protection as he was previously given".
Rather, Ms Fatima said, his legal submissions argued that he should have been told how the decisions about his security were being made.
Prince Harry claimed he had not been given the chance to make his own case or see risk assessments that might have been carried out.
He also referenced security incidents that have happened since his security was downgraded.
These include al-Qaeda calling for the prince to be murdered in 2020, and a "dangerous car pursuit with paparazzi" in New York in 2023.
Sir James Eadie KC, representing the Home Office, said it was "important to emphasise" that the security previously given to the prince had not been fully revoked.
He said, instead, it had been decided that the security "would not be provided on the same basis as before" due to the duke's "change of status" and his moving abroad.
In written submissions, Mr Eadie said the prince's appeal involved "a continued failure to see the wood for the trees".
He added that Prince Harry's argument was based on "only reading small parts" of the evidence and the previous judgement, and doing so "out of context and ignoring the totality of the picture".
Mr Eadie said Ravec had treated the claimant "in a bespoke manner", adding: "He is no longer a member of the cohort of individuals whose security position remains under regular review by Ravec."
In 2023, Prince Harry also lost a legal challenge in his bid to be allowed to make private payments for police protection.
While most of the proceedings are set to be held in open court, confidential information about security arrangements and threat levels will be heard in private.
A written decision will be issued at a later date.
