During the five-or-six-second descent he estimated he probably reached a speed of more than 80km/h.
The sensation was like flying, he said.
"I had a great time doing it."
However, the route was not for the inexperienced - not only because of its 34.8 per cent gradient - but also due to bumps in the road.
"The most challenging part of that hill is all the different connections of concrete.
"They're the bits that degrade and there's significant gaps that really send quite significant jolts up through your board."
From the top of the street he had a good view of traffic to gauge conditions and also had two spotters, he said.
"I was pretty confident with my ability to be able to get down, otherwise I don't think I would ever attempt that - it's all about evaluating the risk."
He may also have set a record, he believed.
He knew of others who had skated Baldwin St from top to bottom, shifting their weight while descending to reduce speed.
To his knowledge he was the first to have "bombed it'" - skating straight and going as fast as possible.
Mills-Goodwin was travelling in New Zealand but was set to depart for Argentina to compete in the World Skate Games later this year.
He had been selected to represent Australia in the skateboarding category, he said.
"I've been travelling all over the world to go to different places, skate the big roads and go really fast - it's something I just really love doing."