The Law and Order: SVU actor will take to the stage at the Peacock Theater in Los Angeles on 14 September to present the annual awards for television, and hailed it a "great honour" to be involved in the telecast, particularly in a milestone year for broadcaster NBC.
She said in a statement: "Bringing important stories into the light has been the heartbeat of my career. It's my great honour to host the 78th Emmy Awards - in the 100th birthday year of my beloved NBC - and celebrate this extraordinary community of storytellers.
"Whether it's an actor or a director, a costumer or a sound designer, we are all so privileged to take part in creating television that unites us.
"Regardless of how, where or when we watch, we are together in our laughter, our tears, our love of stories - and our delighted anticipation to see what happens next."
NBC/Peacock were delighted to have secured the services of a television "icon", executive vice-president Jen Neal said.
"Few performers have left the kind of mark on television that Mariska has," she said in a statement.
"As NBC celebrates 100 years of unforgettable storytelling, we can't think of anyone more fitting to help celebrate the incredible legacy of television."
Jane Lynch was the last woman to host the Emmy awards, for Fox in 2011, and only two other women have fronted the ceremony in the past century.
Ellen DeGeneres took the reins in 2001 and 2005, and Heidi Klum was part of a presenting team that also included Tom Bergeron, Howie Mandel, Jeff Probst and Ryan Secrest in 2008.
Nominations for the Emmy Awards will be announced on Wednesday.
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