TransGrid chief information officer Tony Meehan told ZDNet Australia the company would sign the deal with the Brisbane-based outsourcer on Tuesday.
The contract includes an option for an additional three years.
The decision marks a departure from TransGrid's previous selective sourcing model and is a blow to Fujitsu.
For the last five years, Mincom and Fujitsu have been TransGrid's key vendor partners. Mincom has been responsible for application support and help with its Ellipse ERP suite, used by TransGrid, while Fujitsu has managed infrastructure such as desktop, server and network support, as well as service desk.
"In the marketplace up until a few years ago, for our size, [we] didn't see many companies that could do all outsourcing in one. So we saw the benefits of selectively sourcing," said Meehan.
"What we did in this tender was see that there was now an opportunity to consolidate to a single outsourcer.
"In some senses, we're going against what a Gartner would say now, 'go selective'.
"Well, we would see that for us, as roughly 1,000 seats, and with a strong drive on process now we're looking to get agility ... we see only benefits now in going to a single provider for our size."
Mincom was chosen over Fujitsu as "the best value bid", Meehan said.
"The reasons we've selected Mincom is they've got the right capability. And we'll work with them now around the Microsoft platform [set] of tools."
The contract follows TransGrid's public tender in April for a master services agreement. TransGrid received four "strong" responses, according to Meehan.
TransGrid's current outsourcing contracts with Mincom and Fujitsu are set to expire at the end of October.
Meehan would not reveal the exact value of the contract.
Mincom did not respond to requests for comment before time of publication.