Milligan joins EY with more than 25 years of tax advisory experience within the professional services industry, including more than 10 years in PNG.
He will lead EY's PNG tax practice, working with national and multinational clients doing business in the region across a wide range of industries including oil and gas, infrastructure, mining, real estate and construction.
EY PNG managing partner Frank Bouraga said: "Colin's appointment reflects the growth and opportunities we have seen in our PNG practice since the opening of our new office in Port Moresby in 2012.
"Colin brings with him a wealth of local market knowledge and experience, as well as a proven track record in providing clients with strategic tax solutions.
"I am delighted to welcome him to the EY PNG team."