Following "careful consideration of potential cross-ownership interests and vertical relationships", the ACCC will not oppose the proposals, it said.
The two bidders are known as the IFM consortium and the QIC consortium. IFM is an Australian pension fund investor, while QIC is the investment arm of the Queensland state government.
IFM already owns a 35% interest in Sydney's two ports, and a 26.7% interest in the Port of Brisbane, where QIC manages a 26.7% stake on behalf of a client. Other members of the consortia also have their own interests in Australian ports and port users.
After "extensive enquiries" with port users and stakeholders at different levels of the supply chain, the ACCC "formed the view that neither acquisition would result in a substantial lessening of competition," said ACCC chairman Rod Sims.
"The ACCC identified several constraints on the consortium members' ability to discriminate in favour of these downstream port services providers or to share commercially sensitive information regarding rivals of these providers," Sims said.
"Further, no single consortium member will control the port, or has a controlling stake in other ports or vertically related businesses. The existence of other significant shareholders in each business limits any potential competitive detriment," he said.
Privatisation of the Melbourne port, the largest general cargo terminal in Australia, is expected to raise AU$5.3 billion ($4 billion), Reuters has reported.