Crossbench senator Bob Day believes he's got more than a strong chance of successfully challenging new Senate voting laws.
The High Court on Tuesday reserved its decision after both sides finished presenting their cases to the full bench.
Senator Day expects an outcome by next week, with the court indicating it was aware May 11 is the last day a double dissolution election can be called.
"I couldn't be happier," he told reporters.
"Whatever the result ... we've had a really good fair go."
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Under the new laws, voters will be able to allocate their own preferences above the line.
If they choose to vote below the line, they will only have to number 12 boxes - not every single one, which can be more than 100.
The Family First senator believes the changes, passed in March, are unconstitutional.
"The effect for many millions of voters is that their vote will exhaust, their vote will die, and they are not informed of that," he said.
"The High Court is now fully aware of that and they've reserved their decision, which we expect will be within the next week."
He said the government tried to "whitewash" his case with its lawyers only briefly responding to his arguments.
