While traditional accountants were blocked from doing face to face meetings during the lockdown Hnry's online service was able to continue functioning.
Fuller said it started working with its banking provider National Australia Bank, parent of the BNZ, in September to line up its move into Australia.
But it had to make a tough call whether to go ahead with it in March as the pandemic saw global lockdowns and dire economic predictions.
"When the pandemic hit and everyone went into lockdown we had a bit of a choice which was either we stop what we are doing and say look we don't want to do this now or we actually take the opportunity and say we know the problems being faced by the self-employed are not confined to NZ, not restricted to whether or not there is a pandemic happening.
"We actually pushed harder and said we absolutely want to do this."
It had been in the process of hiring extra staff for its Sydney office in March but decided to put that on hold.
"We put a bit of a pause on recruitment but that is hopefully going to start up again soon."
Once Australia opened up to travel again, Fuller said he and other co-founders would look to go back there.
Fuller said Australia's similar tax system was one reason it decided to expand there but it was also getting feedback on its Facebook page from Australians who wanted to use the service.
"Through the last year we had people who were crying out for our service. We had people on our Facebook page nagging us every week saying when are you coming over.
Fuller said the business had seen huge growth since its launch four years ago.
"We were working as freelancers and contractors ourselves at the time, and we just wanted to focus on our clients and do great work, but suddenly we had to think about tax calculations and payments, or 'reconciling' in complex accounting software; we had to go and visit an accountant to 'talk about our taxes' - which mean a lot of stress and hassle.
"We knew when we started Hnry that this was a global problem - it's something that freelancers, sole traders and contractors have had to put up with for years".
The business has gone from one person unpaid full time to now be a staff of 18, 19 people and is looking to hire for another three or four roles.
Last year it raised capital from existing investors and also attracted investment from venture capital firm Equity Venture Partners to help pay for the expansion.
Fuller said it was not currently looking to raise capital but would probably do so again next year due to its fast growth.