In a wet and windy capital, yesterday was probably the brightest for him.
Even getting a second chance to plead your case in front of the Court of Appeal is unusual.
Justice John Wild, one of the three judges on the imposing bench, noted the court was reluctant to ever recall a formal judgment and asked why they should.
On behalf of Mr Banks, David Jones QC responded: "It's the right thing to do."
"It's a matter of justice ... You have a situation when Mr Banks succeeded on appeal. This court has made a decision based on a wholly false premise. Thankfully it granted the appeal," Mr Jones said.
"The question has to be asked: Would we have ever known about this complete change of circumstances if this court had not granted the appeal?"
The QC was referring to the fact the Crown did not disclose new material, known as the Butler memorandum, ahead of the previous appeal hearing in October.
Then, two American businessmen gave affidavits which corroborated the evidence of Mr Banks and his wife Amanda and was "likely to have changed the outcome of the trial" if accepted.
The undisclosed evidence in question is a memorandum written by lawyer Rowan Butler who was instructed by Crown prosecutor Paul Dacre, QC, to interview Kim Dotcom about the affidavits filed by the Americans before the appeal hearing. The pair said they arrived in New Zealand on June 5, 2010 and were taken to Dotcom's Coatesville mansion, where they had lunch with Mr and Mrs Banks and Dotcom and his wife Mona. Nothing about electoral donations was discussed, according to their affidavits.
This is at odds with evidence given at the trial, where the Crown contended the lunch was held on June 9, 2010 and the presence of the Americans was denied by the Dotcoms, as well as their bodyguard Wayne Tempero.
The defence was able to prove at the trial there was no lunch on June 9, because Mr Banks was campaigning and Mrs Banks was at work.
In finding Mr Banks guilty, Justice Edwin Wylie said Dotcom was a good witness but was wrong about the date of the lunch and ruled it must have happened on June 5.
But when interviewed by Mr Butler about the new affidavits before the Court of Appeal hearing, Dotcom accepted the evidence of the US businessmen - including that donations were not discussed at the June 5 lunch. Instead, he said there was a second lunch - again on June 9 - at which the donations were discussed.
Dotcom has now signed a new statement for the Crown which contradicts his previous evidence, which Mr Jones told the Court of Appeal means the prosecution faces "insurmountable" problems.
He said the Court of Appeal should have been made aware of the existence of the Butler memorandum at the time of the appeal, because the Crown submissions were made on a false ground.
"This court was denied the opportunity to consider the matter fully. Why should Mr Banks suffer another minute?" said Mr Jones.
"The appellant and the court have been kept in the dark. By the Crown. Critical information which must have made a difference to the outcome."
Mr Jones said Dotcom's new statement confirms there was a second lunch.
He read parts of the transcript of Dotcom's evidence from the trial where Dotcom was asked about the presence of the businessmen at the lunch where donations were allegedly discussed.
"There were no two Americans, that was a total fantasy ... certainly not, no no," Mr Jones quoted Dotcom as saying.
Mr Jones said Dotcom was very specific in his evidence.
"He had ample opportunity to say there was a second lunch. He's said the Americans at the lunch was a 'fantasy' and a nonsense," said Mr Jones.
"That, in my submission, is what his latest statement is."
Other witnesses at the trial, Mona Dotcom and Dotcom's bodyguard, Wayne Tempero, did not say a "dickey bird" about a second lunch, said Mr Jones, and have not made new formal statements following Dotcom's new evidence.
In opposition to Mr Jones was the most senior Crown lawyer in the country.
The Solicitor-General, Mike Heron, QC, appeared by video-link and maintained that while Kim Dotcom's evidence against Mr Banks has changed since the first trial, the story remained the same in one crucial respect.
The Butler memorandum did not change the key plank of the false electoral charge, said Mr Heron.
"Dotcom maintains there was a conversation with Banks in his house about donations. There is no fundamental change about whether there was a conversation. Mr Banks himself accepts that.
"Mr Banks knew that these donations had been made. He knew who the donor was. Whether there was one lunch or two, cannot totally undermine that," said Mr Heron.
This was backed by the corroborating evidence that the two cheques were made out for $25,000 each.
Mr Heron said he was "not defending Mr Dotcom's credibility for one moment" but a judge could rely on parts of his evidence and dismiss others, as Justice Edwin Wylie did when he convicted Mr Banks.
Mr Heron said there was also an issue around whether the Butler memorandum needed to be disclosed to the defence and, in any case, the material did not change the key tenet of Dotcom's evidence.
For the Court of Appeal to rule there was a miscarriage of justice, Mr Heron said there had to be a fundamental error in procedure.
"It's a high threshold and it's hard to see how the lack of disclosure of a statement, which is not crucial to the Crown case, meets that."
With respect, Mr Heron said the trial judge Justice Edwin Wylie, not the Court of Appeal, was the finder of facts in the case.
It was at this point that Justice Forrest Miller jumped in. "That misconceives our position. We were asked to make ruling on evidence found at trial, with one exception - the key witness now concedes a central part of defence case."
He had earlier mentioned that he was "troubled about the basis on which we were allowed to conduct the appeal".
The final words went to Mr Jones. "It boils down to one question. Against a background of evidence at trial and appeal, if this additional material had been known, would a retrial be ordered? That's the litmus test."
Then, two hours after it began, Mr Banks' 37th day in court was over and the Court of Appeal retired to consider its ruling. The decision is reserved but expected to be released this week or next.
Mr Banks said he would respect the decision.
The story so far
April 2012:
Kim Dotcom's $50,000 in anonymous donations to John Banks' mayoral campaign in 2010 becomes public.
July 2012:
Police say they won't lay charges after investigation.
November 2012:
Graham McCready takes private prosecution against the Act MP.
October 2013:
Banks resigns as a minister after Judge Phil Gittos rules he should stand trial.
June 2014:
Banks is found guilty after a High Court trial. He later resigns from Parliament.
November 2014:
Banks is successful in overturning the conviction in the Court of Appeal.
January 2015:
Solicitor-General Mike Heron, QC, confirms a new trial. Scheduled for July.
March 2015:
Banks' lawyer, David Jones, QC, seeks to have charge dismissed after the late disclosure of new material from the Crown. Now seeking Court of Appeal to recall its ruling which ordered a new trial.
Yesterday:
The case goes before the Court of Appeal and the judge reserves his decision.
