Hardy was initially supposed to face Jarjis Danho in Singapore on Oct. 26, but per Okamoto, Danho pulled out of the bout.
The 6'5", 265-pound Hardy has a 5-1 professional MMA record, with all five of his victories coming via knockout or TKO. His loss occurred via disqualification (illegal knee).
Sosoli, 29, is 7-2 with one no-contest, which occurred in his most recent bout against Dustin Joynson on Aug. 27. He took part in The Ultimate Fighter 28 and is a Contender Series alum.
Sosoli has never fought in the UFC.
Hardy's most recent fight ended with a 45-second TKO of Juan Adams at UFC San Antonio in July.
The bout will occur on the UFC Fight Night card, which is headlined by a light heavyweight matchup between Dominick Reyes and Chris Weidman. Maycee Barber and Gillian Robertson will take part in a women's flyweight fight that featured two of the top-15 ranked fighters in the division.
TD Garden will be the host for the event, which is slated to begin 9 p.m. ET.