New York needed a roster spot to activate linebacker Brandon Copeland, who is returning from a four-game suspension for violating the NFL's policy on performance-enhancing drugs.
Falk completed 64.4 percent of his passes for 416 yards and three interceptions in three games. He did not throw a touchdown pass.
Falk was forced into the action when Darnold and Trevor Siemian (ankle) suffered injuries.
He completed 20 of 25 passes for 198 yards in relief of Siemian in Week 2 against the Cleveland Browns but struggled in his two starts. Falk was sacked 14 times and threw for just 218 yards -- 98 in a 30-14 loss to the New England Patriots and 120 in last week's 31-6 setback against the Philadelphia Eagles.
He committed four turnovers against the Eagles, with an interception and fumble off a strip sack being returned for touchdowns.
Copeland, 28, had 35 tackles and five sacks last season in his first campaign with the Jets.
He has denied that he knowingly took a banned substance and has vowed to file a lawsuit against a company that gave him what he termed "contaminated supplements."
--Field Level Media