John Woodcock accused the party of “allowing its disciplinary process to be tainted and open to charges of rigging”.
He strongly denies the accusation of sexual harassment but says he understands the probe has to be “thorough and fair”.
In a letter to Jennie Formby, Labour’s general secretary, Mr Woodcock accused her of having a “disregard for the law” by not providing an update on the investigation’s progress.
He said he had been forced to take her to court to “comply with the basic legal responsibility”.
Mr Woodcock has demanded that an independent official be appointed to lead the inquiry instead.
Ending his letter, the Barrow and Furness MP said he was making the document public as a “pre-emptive step” given the “recent experience of Labour officials leaking private information to damage me”.
Mr Woodcock, who is an arch critic of Labour leader Jeremy Corbyn, was suspended by the party in May.
The Sunday Mirror reported he was alleged to have sent inappropriate texts and emails to a former female staff member between 2014 and 2016.
He was first elected to parliament in 2010 and was a shadow transport minister between 2010 and 2013.
A Labour Party spokesperson said: “The Labour Party takes all complaints of sexual harassment extremely seriously, which are fully investigated and any appropriate disciplinary action taken in line with party rules and procedures. The process is the same for everyone.
“We are determined to challenging and overturning sexual harassment and misogyny within politics and the corridors of power, and across society as a whole.”