Successful completion of the program will lead to Dareus' charges being dropped and, under a new Alabama law, his criminal record being expunged.
The NFL will also monitor Dareus under its substance abuse program. Dareus was charged with criminal possession of a controlled substance and possession of drug paraphernalia following a traffic stop in Alabama.
Dareus' attorney, Rod Giddens, said a judge commended Dareus for accepting responsibility for his actions. Giddens also said the officer who arrested Dareus "raved" about how cooperative Dareus was with police.
Coach Doug Marrone excused Dareus from training camp to attend the court hearing in Alabama. He re-joined the team at St. John Fisher College on Monday evening.
"After dealing with a personal matter in Alabama, I am excited to return to training camp to rejoin my teammates in our preparations for the 2014 season," Dareus said in a team-released statement. "Right now, my focus is on earning the trust of my teammates, coaches and the fans while continuing to improve as a football player. I have a passion for this game and I want to be here to help this organization achieve its goals.
"There are things I need to work on professionally and personally to make sure I can be accountable to myself, my family, this team and this community. My focus will remain on achieving that goal one day at a time. I want to thank the Bills organization, coach Marrone and the coaching staff, my teammates and our fans for their continued support."
However, Dareus has yet to pass his conditioning test and won't re-take the conditioning test until at least Thursday, a team source told ESPN's Sal Paolantonio. He remains on the active/non-football injury list.
"He'll be like everybody else on the side training getting ready to pass the physical," Marrone said Monday. "He's one of the players that didn't pass the running test."
The failed conditioning test was the latest setback for Dareus, who, in addition to his arrest in Alabama, faces misdemeanor charges in Hamburg, New York in connection with a street race in May. His next court date for those charges is in September.
Marrone, however, was optimistic about Dareus on Sunday.
"He'll be in shape and ready to play," Marrone said. "Right now he needs to focus on getting himself ready, getting himself on the field, and focus on football.
"I think that's what he'll be ready to do and that's been my conversations with him."