Miami announced the historic hire on Friday, with Ng believed to be the first woman hired as a general manager in any of the four men's major sports leagues in North America.
"I entered Major League Baseball as an intern and, after decades of determination, it is the honor of my career to lead the Marlins as their next general manager," Ng said.
"We are building for the long term in South Florida, developing a forward-thinking, collaborative, creative baseball operation made up of incredibly talented and dedicated staff who have, over the last few years, laid a great foundation for success.
"This challenge is one I don't take lightly. When I got into this business, it seemed unlikely a woman would lead a major league team, but I am dogged in pursuit of my goals.
"My goal is now to bring championship baseball to Miami. I am both humbled and eager to continue building the winning culture our fans expect and deserve."
Ng has over 30 years of experience in MLB having worked with the Chicago White Sox, New York Yankees and the Los Angeles Dodgers, serving as assistant general manager for the latter two.
Since 2011, Ng has worked as senior vice president of baseball operations for MLB.
She now takes the reins of the Marlins front office after a 2020 season that saw them reach the playoffs for the first time since their 2003 World Series win.
The Marlins went 31-29 in a campaign shortened by the coronavirus pandemic, beating the Chicago Cubs in the National League Wild Card Series before being swept by the Atlanta Braves in the Divisional Series.