Wilder (42-2-1) was stopped in the 11th round by Fury in Las Vegas for his second straight loss to the Briton, who retained the WBC heavyweight title. Their first fight in December 2018 ended in a split draw.
"It's been a long journey for me and as of today it continues," the American, who was honoured with a statue in his hometown of Tuscaloosa, Alabama earlier this year, said in a statement on Wednesday.
"I thought so many times about whether I should stay out of the business or come back. Once I got my statue in my hometown and saw so many people arrive and celebrate with me ... made me feel like my job is not done."
The fight will take place at Brooklyn's Barclays Center, the setting for Wilder's knockout wins against Dominic Breazeale, Luis Ortiz and Bermane Stiverne.
Helenius (31-3) last fought on the card of the third Fury-Wilder fight, securing a sixth-round win against Poland's Adam Kownacki.
"I've been waiting for this opportunity for a long time and I'm going to be ready," said the Finnish.
"I'm going to produce an even bigger upset than I did with Kownacki. I'm going for the belt, so this is a fight to prepare me to achieve that goal."
