Our Idiot Brother is a story about a young man with three successful sisters. Paul Rudd plays Ned a farmer who grows and sells his own organic foods. Ned is somewhat of a non-conformist and lives life as a free spirited hippie who sells his produce at local markets. On one particular occasion, he is approached by a police officer at the market who is looking to purchase some marijuana. Ned's unfortunate choice to give him what he wants lands him in jail. When he is finally released he goes back to the place where he was living with his girlfriend only to find out she has a new boyfriend and has taken over his farm.
Having no place to go, Ned decides to stay with his mom. In an effort to celebrate her son returning home she invites his sisters to a dinner. His sister Liz wants to help him get back on the right path and extends an open invitation to stay with her whenever he wants to. He does take her up on this offer and pays her a visit. When Ned was released from jail, he was also given the name of a parole officer he was to meet with. The relationship between Ned and his parole officer develops into a friendship where the officer often provides advice and counsel to help Ned turn his life around.
While staying with his sister Liz, Ned ends up working with her husband Dylan. Dylan does not care for Ned and puts pressure on Liz to kick him out. She refuses to do so until she discovers that an interview her son had with a representative from a prestigious school did not go the way she had hoped. Her son disclosed information about Ned which included his arrest for drugs. This upset Liz so much she finally kicked him out.