In a judicial review application filed on April 1, Najib said an "addendum order" issued by the former king had accompanied a pardons board's decision in February to halve his 12-year jail sentence for graft in the multibillion-dollar 1MDB scandal.
Najib had sought for the court to compel the government to reply to or confirm the existence of the royal order, which he said would entitle him to serve the remainder of his term under house arrest, and to execute the order if it existed.
In a copy of the judgment released to media on Wednesday, the Kuala Lumpur High Court found there was no arguable case warranting a full hearing of Najib's application.
Judge Amarjeet Singh described affidavits filed by Malaysia's Deputy Prime Minister Ahmad Zahid Hamidi and another high-ranking politician from Najib's party saying they had seen a copy of the royal order as hearsay, and said the government had no legal duty to respond to the application.
Najib planned to appeal the decision, his lawyer Muhammad Shafee Abdullah told reporters.
"In terms of ethics, the government should have answered," he said.
The pardons board that halved Najib's term was chaired by King Al-Sultan Abdullah Ahmad Shah, whose five-year reign as head of state ended in January.
Najib was found guilty in 2020 of criminal breach of trust and abuse of power for illegally receiving funds misappropriated from a unit of state fund 1Malaysia Development Berhad (1MDB). The verdict was upheld by Malaysia's top court in 2022.
Malaysian and U.S. investigators estimate $4.5 billion was stolen from 1MDB and more than $1 billion channelled to accounts linked to Najib.
The pardons board in February said Najib was expected to be released in August 2028, six years after he began serving his sentence. It also reduced fines imposed on the ex-premier, sparking uproar in Malaysia.
Najib, who is also considering filing a new petition for a full pardon, remains on trial for corruption in several other 1MDB-linked cases.
