The veteran left-hander was recently released by the Chicago White Sox after having a 2-5 record with a 7.88 ERA through eight starts. He was in the final season of a $55 million, three-year deal.
The 34-year-old Keuchel won the American League Cy Young Award with the Houston Astros in 2015 and is also a two-time All-Star and five-time Gold Glove winner. He'll try to recapture his old form by reuniting with pitching coach Brent Strom, who was with the Astros in 2015 and joined the Diamondbacks during the offseason.
The Diamondbacks are looking for more options in their starting rotation after right-hander Humberto Castellanos went on the injured list because of an elbow injury.
If Keuchel is added to the 40-man roster, Arizona would be responsible for only a prorated share of the $700,000 major league minimum, and the White Sox would remain responsible for the rest of his $18 million salary this year. Chicago also owes a $1.5 million buyout of a 2023 option.
Keuchel, 101-87 with a 3.86 ERA in 262 career games with 251 starts, last appeared for Chicago on May 26, when he lasted just two innings, allowing seven hits and six runs in a 16-7 loss to the Boston Red Sox.
The Associated Press contributed to this report.