Clad in three layers of thermals, wet suit and booties and daubed with petroleum jelly to withstand the 14degC water temperature, the 31-year-old slipped into the Kingston waters at 8.45am on Saturday.
Eighteen hours and 42 minutes later, under the cover of darkness, he arrived in Glenorchy.
The National Health Committee policy analyst has a background of competitive swimming as a youth and turned to distance swimming while recovering from a snowboarding injury.
What makes his achievement all the more remarkable is the fact he reached his goal despite suffering from motion sickness - the very reason his last attempt failed.
When the wind picked up during his 2009 attempt, nausea from the waves forced him from the water and is the reason he has never been able to tackle Cook Strait.
Mr Campbell-MacDonald had not thought he would be able to make it to Glenorchy, the equivalent of three crossings of Cook Strait.
"The idea was to make it to Queenstown [35km] and then decide whether I could take it to Glenorchy and I was pretty sore, but the conditions were perfect and there's no guarantee I would ever get this chance again so I pushed on."
A support boat and Zodiac followed him, with friends feeding him baked potatoes and energy drinks every half an hour and tracking him in the dark using glowsticks attached to his wet suit.
As he neared Glenorchy, the glacial waters of the Dart River further cooled the lake temperature to 12degC, meaning he was soon fighting hypothermia, as well as a bout of nausea.
"When I got out, I guess I had moderate hypothermia but I had been swimming for a long time, so I was stumbling around a bit," Mr Campbell-McDonald said.
"There was a bit of relief, but at that stage it was more about making sure I was OK than celebrating."
A day of rest, several glasses of Champagne and a few painkillers later, Mr Cambell-MacDonald has had time to recover and was proud of his record-breaking achievement.
"With distance swimming, people are competitive about going the furthest, being the first, the youngest ... It had never been swum and it's the longest lake in the country, so it's my first."
He now plans to "hang up his togs", apart from taking part in the New Zealand Ocean Swim Series, the next leg of which he will miss while he recovers.
