Fetching coffee and helping out around the office turned into a fulltime job booking artists for concerts and festivals such as Field Day, Parklife, Harbourlife and Shore Thing.
"I got to know and understand the festival business from the inside out, which really helped me in the long run," Constantine told news.com.au.
"I started as a touring intern, literally doing anything that an intern would do in any office job but working on the touring side of the business, dealing with artists, helping put together artist packages and club tour runs, working on-site during the festivals, building up the artist riders."
A rider is the industry term for the list of dressing room requirements that performers demand as part of their contracts.
Some entertainers are known for their highly specific and diva-like requests, with artists like Katy Perry, Lady Gaga, Van Halen and Kanye West having reportedly demanded items including imported Versace towels, ornate French lamps, a mannequin with puffy pink pubic hair, mini Babybel cheeses, Haribo gummies and M&Ms with the brown ones taken out.
"There were definitely some strange things coming up on rider requests, and probably a few that I shouldn't mention!" Constantine said, declining to name names.
But he said most artists were understanding when he explained that it would not be possible to track down a specific brand of chewing gum or fried chicken not available in Australia.
The most satisfying moment, he said, was when an emerging artist he'd booked for a festival went on to achieve superstardom.
ARIA award winner Flume had just won Triple J Unearthed when he was booked to play the small stage at Field Day in 2012. Two years later, he was the headline act.
"Standing on the main stage with him and seeing 25,000 fans enjoying that was pretty amazing," Constantine said.
"It was goosebumps on the arms and hairs standing up ... To see that progression to where he's at today in his career was something pretty amazing."
After finishing his Media and Communications degree in 2012, Constantine flew to Los Angeles on a J-1 visa, taking some time to travel and "get a bit of a feel for the music" while freelancing as a tour manager.
"Then I was offered a number of different jobs with a few different companies, and ended up eventually saying yes to working with Smirnoff," he said.
His current role centres on promoting the brand's message of inclusivity through projects like the Smirnoff Sound Collective artist mentorship program, and hosting a #lovewins fundraiser at Orlando's Pulse nightclub after the September mass shooting in which 49 people were killed.
"Everything we do as a brand is centred around inclusivity, we use music as a way to move the world to be more inclusive," he said.
"We have a voice within music because Smirnoff is a brand that's kind of synonymous with music around the world."
Working for a big multinational was "a big learning curve" after cutting his teeth in a small Australian company, he said.
And while he couldn't have predicted where his career would end up, going after his area of passion had paid off.
To be in New York - where he had once hoped to attend music school - using his degree in the entertainment industry was "a dream".
"It all just kind of tied in and shaped together ... It was kind of just an evolution rather than saying 'this is something I've always wanted to do'."
