Harmon had sought custody of his nephew, Sam Nelson, the grandson of Harriet and the late Ozzie Nelson, claiming his sister's addiction to prescription drugs impaired her ability to take care of the boy.
Kristen Nelson had won custody of Sam and his siblings after she and Rick Nelson were divorced in 1982. Rick Nelson died in a plane crash in 1985.
"Today, Mark was the same little brother who I used to push into the water at Lake Arrowhead because he was afraid of the catfish," Kristen Nelson said. "He's afraid of the catfish out here."
Sam cried when he was told of the agreement.
Harmon said he agreed to the settlement because the battle was ripping his family apart.
Dawber tried to avoid reporters before leaving the courtroom before noon to go to a rehearsal.
"I'm not afraid to get back" on the witness stand, Dawber said. "I came here today, didn't I?"
Although the boy went home with his mother, he is expected to spend a lot of time with Harmon and Dawber.
Under the settlement, the whole family is expected to go to therapy with Sam, including his mother; twin brothers Matthew and Gunnar; sister Tracy; Harmon, Dawber, uncle David Nelson and the three grandparents, said Harmon's lawyer, Lawrence Stone. Sam's maternal grandfather is sports announcer Tom Harmon.
