Vocus has become TransACT's primary IP transit provider in a deal worth over $500,000.
Vocus' chief executive, James Spenceley, told iTnews the win has been over 12 months in the making.
"We were dealing with TransACT around the time of our inception," Spenceley said.
"We were targeting them as one of the top ten companies we wanted to be dealing with. We got quite close [to winning the business] this time last year but the issue for them was we were too new and unknown."
TransACT said its fibre optic network is available to over 90,000 householders in Canberra and surrounds.
It also said 1,500 businesses are connected to its network.
Spenceley would not be drawn on which transit providers TransACT had "consolidated" in favour of Vocus.
But he claimed Vocus was winning business by being "cheaper than the incumbents" and offering a higher grade of engineering support.
He also expected the deal would open other doors in the market and said the company would announce additional IP transit wins shortly.
TransACT has been contacted for comment.