The businesses will be integrated under the leadership of Simms CEO, Danny Moore, and all staff from both sides will remain with the merged business.
He will report to the Express Data board along side its CEO, David Gage.
The combined team will be about 77 staff strong with Simms moving into Expressonline's Botany office.
Expressonline general manager, Siobhan Delaney-Miller, will now head up the operations of the merged entity.
"All staff are vitally important to us because we want to grow," Express Data Holdings director, Ross Cochrane, said.
The companies expect to become fully integrated by September 1, with Simms coming under the Expressonline banner.
"We think the integration will be fairly smooth and we really believe that for our vendors and resellers, they should expect to see business as usual and more resources available to them," he said.
Cochrane said it had been looking to grow the business for some time.
"We had been growing the business successfully, but we wanted to accelerate our growth and what we found in Simms was a very complementary business fit for Expressonline," Cochrane said.
"We felt the cultures of the businesses and leadership of Simms were aligned with the way that we operate in the market."
Simms CEO, Danny Moore, said it was constrained by financial capacity to keep growing at the rate that it wanted to grow.
"We've grown at such a rate in the past four to five years, and to be able to continue that rate of growth we needed to look at financially restructuring the company. We're a private organisation and we were starting to miss out on opportunities without the significant financial restructuring of the organisation," Moore said.
"With Expressonline, we've been friendly competitors for some time and we complement each other perfectly. They've got a very strong online model and financial backing, their infrastructure and logistics capability is industry leading."
All of the vendors represented by both Simms and Expressonline will continue as valued partners. Both distributors carry Apple products in their line-up, and expect the combined business will hold the largest market share in the distribution channel.
The combined entities in the Express Data group have the scale, vendor partners, structures and leadership to drive $1 billion in sales across ANZ in 2012, according to a statement.
Cochrane didn't rule out further acquisitions down the track.
"We're serious about the distribution business in the market and we're prepared to make investments because we're getting the returns in the distribution market that we expect," Cochrane said. "Should appropriate investment opportunities come up in the future, we'll look at those very carefully again."
Simms began trading in 1995 and currently services more than 3000 retail and reseller customers across A/NZ.
Expressonline was established in 2004 and through the use of shared back end facilities with Express Data and cost effective systems, it can deliver both quality and cost efficiency that allows the channel model to be very attractive to vendors.