Mr O’Sullivan said he took the unusual step after the government twice voted down a motion to hold a joint sitting of Parliament to allow him to take his seat in the Legislative Council last week.

He said his lawyers had written to Premier Daniel Andrews informing him of “his constitutional duty to hold a joint sitting of the Parliament”, but had not received a response.

“The constitution says that a joint sitting must be held and the constitution says there must be 40 members in the Legislative Council so at the moment Daniel Andrews is in breach of the constitution,” he said.

Mr O’Sullivan was officially nominated by the Nationals in late July, to fill the vacancy left by Damian Drum, who moved into federal politics after the election.

Labor voted against holding a joint session after Special Minister of State Gavin Jennings was suspended for six months from the upper house earlier this year for failing to provide documents, some of them cabinet-in-confidence.

Mr Andrews has previously said the government would only vote to approve the joint sitting once Mr Jennings had returned to Parliament.

"I think we are very keen to have a joint sitting where the Leader of the Government in the upper house [Mr Jennings] is there, and this is entirely a matter for the upper house and the Liberal Party and others to deal with,” he said. 

But Mr O’Sullivan said the Premier’s actions amounted to a “revenge act” for the unrelated matter which led to Mr Jennings’ suspension.

“Even though the Gavin Jennings issue is very different and not related to me entering the Parliament, they are refusing to hold a joint sitting in retaliation for that, which is denying the people of northern Victoria their rightful representation and their vote in the Legislative Council,” he said.

Mr O’Sullivan said the impasse had made it impossible for him to start work as a member of Parliament.

“I can’t open an electorate office, I can’t employ staff, I can’t get an email address or get my IT systems up and running, but most importantly I can’t get out there and start to represent the people of northern Victoria on the issues that are very important to them,” he said.

A government spokesman said, as the government’s leader in the upper house, Mr Jennings would be pleased to move the motion appointing the new member for Northern Victoria upon his return to parliament.

He said the government would welcome the assistance of the Leader of the National Party to enable this to happen as soon as possible.

“For months the government has been working to broker an agreement with the Coalition opposition to see the return of the democratically elected Member for South-Eastern Metropolitan to the Parliament, after he was suspended for an unprecedented six months by a Liberal-National-Green coalition for merely doing his job,” the spokesman said.

“We want to see this situation resolved as soon as possible. However to do so requires the cooperation of the Liberals and Nationals. We would welcome Peter Walsh’s assistance to see both matters resolved in a timely way and ensure the communities in Northern Victoria and South-Eastern Metropolitan are fully represented in the Parliament.”

It is understood the government will argue that the timing of any joint sitting is a matter for Parliament, and not the courts, to determine.

 – with The Age