Martin left the Dolphins last October and complained of bullying. Miami later suspended Incognito, who was alleged to have sent threatening messages containing racist language.
The NFL retained Ted Wells, a New York attorney, to investigate the workplace situation in the Dolphins' locker room.
Wells released his report Friday, saying Incognito, John Jerry and Mike Pouncey "engaged in a pattern of harassment directed not only at Jonathan Martin, but also other young Dolphins offensive linemen and an assistant trainer."
Wells said the trainer was "repeatedly the object of racial slurs and other racially derogatory language" while the unnamed other player was "subjected to homophobic name-calling and improper physical touching."
"Martin was taunted on a persistent basis with sexually explicit remarks about his sister and mother and at times ridiculed with racial insults and other offensive comments," Wells said.
Wells' report refutes charges Martin made up claims of harassment after he left the team.
"The report concludes that the harassment by Martin's teammates was a contributing factor in his decision to leave the team, but also finds that Martin's teammates did not intend to drive Martin from the team or cause him lasting emotional injury," Wells said in a statement.
Incognito this week made a series of postings on Twitter, including: "the truth is going to bury you and your entire 'camp'."
Dolphins owner Stephen Ross issued a statement saying: "We have just received the report from Ted Wells and will review it in detail before responding relative to the findings. When we asked the NFL to conduct this independent review, we felt it was important to take a step back and thoroughly research these serious allegations. As an organization, we are committed to a culture of team-first accountability and respect for one another."
A statement from the NFL Players Association said: "We have received the report on workplace conditions in Miami. We will review the findings closely, confer with our players and all relevant parties involved."