Newman had argued that while Lowe was “becoming a major force, arguably, in politics”, temporarily blocking the ICGS from investigating the complaint would not harm the watchdog.
Sarah Hannett KC, for the ICGS, said that Lowe – who earlier this month announced the launch of a new political party called Restore Britain – was subject to rules and procedures setting out standards of behaviour for members of the House of Commons.
She said it meant Lowe was “answerable to the House” about the allegations, and that it was not “the constitutional role of the court to supervise or interfere with that”.
A separate hearing on whether the court has jurisdiction to deal with the wider legal challenge is scheduled for 17 March.
In his ruling on Tuesday, Mr Justice Chamberlain said the risk of harm to Lowe if the temporary block was not granted had been “overstated”.
He also said it “seems very unlikely” that the ICGS would make any public findings related to its investigation before the March hearing.
“This public interest in the continued operation of the complaints process would be a weighty one in any case, and would be especially so if the claimant is, as Mr Newman says, becoming a major political force,” he added.
The ICGS is responsible for investigating complaints related to bullying, harassment and sexual misconduct within Parliament.
Lowe was elected as a Reform UK MP in 2024 but was suspended by the party in March last year amid claims he had threatened then-party chairman Zia Yusuf.
He denied the allegations, and the Crown Prosecution Service said no criminal charges would be brought against him in relation to alleged threats towards Yusuf.