A jury in 2018 found no defamation had occurred and Arnold was ordered to pay costs, reported to be about $183,000 to each party. However, Arnold could not pay back debtors and was eventually made bankrupt.
More recently, the Department of Internal Affairs (DIA) raised concerns about conflict at the council, following reports of tension among elected members and the council's chief executive.
Shadbolt's health has also been called into question publicly several times, with some councillors saying he was struggling to follow what was happening at meetings.
Now Shadbolt has spoken with the Herald on Sunday about his life, the current challenges at the council and his future plans.
Asked directly about his health and ability to lead the council and city as mayor, Shadbolt admitted "there are certainly things going on" and referred to the stress of his defamation case.
But he played down the DIA investigation as not "much of a problem at all", comparing it to his heyday as mayor of Auckland's Waitematā in the 1980s.
"I suppose I'm a bit battle-hardened," he said. "In Waitematā City we had punch-ups in the carpark and an Audit Office investigation that went on for a couple of years."
Born in Remuera, Auckland, less than two years after the end of World War II, Shadbolt's first foray into politics began in his early youth.
"My first election was getting to be a bus monitor, and then I graduated to a milk monitor," he said.
But at university he started getting more seriously involved in political groups, joining the "Auckland University Society for the Active Prevention of Cruelty to Politically Apathetic Humans".
"I became president of that organisation, getting into all sorts of trouble."
Shadbolt was arrested 33 times. "I wasn't an academic success but I had an enjoyable time".
Although he loved being a student, Shadbolt said he "hated being poor".
He took a gap year in the mid-1960s to look for the highest-paying job he could find.
He ended up in Manapouri working on the local power project as a tunneller.
In 1983 he stood for Mayor of Waitematā City and won, but lost a mayoral run in 1989 in newly formed Waitākere City.
In 1993 Shadbolt ran in Invercargill at the request of some of his rugby friends – this time winning.
"I didn't get many votes but there were 21 candidates standing so you didn't actually need to get a lot of votes."
With the exception of a defeat in 1995, and a successful rerun in 1998, Shadbolt has possessed Invercargill's mayoral chains ever since.
"You've got to love the job, you got to love sewage, you got to love water, you got to love inner city upgrades, you got to love events, you've really got to be an outgoing sort of spirit."
Invercargill and Southland were facing some big challenges, including the devastating fallout of Covid-19 on the local events and tourism industries. The announcement that Tiwai Point aluminium shelter, near Bluff, will close in 2021 - with the potential loss of thousands of jobs - has also sent shockwaves through the Southland community.
Shadbolt conceded the current situation was "certainly a bit of a rough patch".
But he downplayed the DIA investigation and issues raised about "significant conflict" within the council.
"I reckon if you get any 12 New Zealanders and locked them in a room for three years and made them spend a billion dollars a year on infrastructure ... they don't know each other, and, especially in the last election, we had a whole lot of newbies on, a whole lot of candidates who want to be the mayor, it is just bad luck - I reckon that the mix wasn't right."
He said the "ambition" around the room was a good thing.
"I'm not criticising them, they want to save the world, they want this, they want that, they're prepared to throw down the gauntlet and have a go, but I have to defend my position.
"Eventually the old fellow will be cornered ... The wolves are circling, and they'll knock you out ... It's a competitive blood sport, local government elections."
On a scale of one-to-10, he rated the effectiveness of the current council "about halfway".
Asked what he believed needed to be fixed, Shadbolt said he didn't want to compromise the DIA investigation. However, a good step would be simple things like heading away as a group straight after an election so everyone could get to know each other – something he said no longer happened.
He said the defamation action brought against him by Arnold – and subsequent appeals – had "dragged on" through his last and current mayoralty.
"I owe lawyers bills of $350,000, and there is just no way I can pay it, so what I am staring down for my retirement is bankruptcy."
He was not facing bankrupt proceedings now. It was reported in March this year Shadbolt and the council were going to court over who would cover costs incurred by the mayor to defend Arnold's lawsuit.
Shadbolt said he walked into the council building sometimes pretending he was really happy, thinking "If you can't make it you fake it."
"I like to think being a comedian and being a councillor is unusual but society needed a few combos like that ... a lot of people hate you for it, they think you are not taking the job seriously. You just feel so devastated ... it's hard to keep that positivity."
Asked if the reason he was still working at 73 years old was because he needed the money, he said "yeah it's a bit of that," before adding that, equally, he loved what he did.
However, Shadbolt said he had no plans to bow out any time soon and planned to run again for the mayoralty.
"I'll come out with all guns blazing."
He also plans to write another book and would like to get back into the film industry – he had a role in The World's Fastest Indian, released in 2005, where he played Frank.
He said his hero was Winston Churchill.
"He was in office until his 80s, and I want to be in office until my 80s - that's what I aspire to."