Optus told the Australian Stock Exchange it would make an off-market offer of 68 cents per share. The Alphawest board has unanimously recommended its shareholders accept the proposal.
"This acquisition is part of Optus executing on our growth aspirations as an integrated ICT provider," the company's chief executive, Paul O'Sullivan, said in a statement.
"It boosts our national presence and complements our areas of existing strength.
"Alphawest has excellent credentials in network consulting, integration and information management service; high quality people and processes; and a track record of delivering high levels of customer satisfaction," O'Sullivan said.
Optus' proposal follows a number of recent acquisitions by competing IT services providers. Last year, IBM acquired local network integrator Logicalis for AU$88.5 million, and Telstra purchased Kaz Group for AU$333 million.
Should the takeover be accepted, Alphawest will operate as a wholly-owned subsidiary under the Optus Business division, according to O'Sullivan.
Alphawest chairman Hugh Beggs said the two companies were "an excellent fit".
"We have partnered extremely well with Optus to date and we welcome the opportunity presented by this offer to enhance our position in the Australian ICT market," he said.
Optus said it already signed a deal to acquire UXC Limited's 19.96 percent shareholding in Alphawest.
The Optus offer is subject to a 90 percent minimum acceptance condition by Alphawest shareholders.