The person spoke to The Associated Press on condition of anonymity Thursday because the deal was subject to a successful physical and had not been announced.
A 31-year-old right-hander, Cishek had a 2.01 ERA and a 3-2 record in 49 relief appearances this year for Seattle and Tampa Bay, which acquired him on July 28. He would join rejoin a rebuilt Cubs bullpen that includes right-hander Brandon Morrow, who finalized a $21 million, two-year contract on Tuesday.
Cishek is 24-28 with a 2.73 ERA and 121 saves over eight seasons.
His eight-year major league career started with the Florida and Miami Marlins from 2010-15. He was traded to St. Louis in July 2015, became a free agent and signed a $10 million, two-year contract with the Mariners.
He had 25 saves for the Mariners in 2016 but lost his closer role after six blown saves. Cishek threw a tying wild pitch as he failed to hold a 6-3 lead in a 7-6 loss at the Cubs on July 31, and the following night he allowed a tiebreaking home run to Boston's Mookie Betts leading off the ninth inning in a 2-1 defeat.
