Stephen England-Hall, chief executive of Tourism New Zealand, said the event will showcase the country.
"The high-profile event will showcase New Zealand as a fantastic host destination and a place where creative thinking is embraced," England-Hall said.
"It is an excellent opportunity for Wellington and New Zealand to show how well we host large-scale global events."
Securing hosting rights has been eight years in the making for co-chairs Norman Cates and Kelly Buehler.
"We are utterly thrilled to bring some of the great names in science fiction to New Zealand to meet their Kiwi fans and to give our amazing creators here at home their time to shine on an international stage," Buehler said.
Worldcon, which was first held in 1939, is the annual convention of the World Science Fiction Society (WSFS) and has run continuously since 1946.
The 2020 event has been named CoNZealand and will be held at multiple venues across the city, including TSB Arena, Shed 6, the Michael Fowler Centre, and Intercontinental Wellington.