The Martin family procures 2005 NDR series robot "Andrew" into their home to perform housekeeping and maintenance duties. He introduces himself by showing a presentation of the Three Laws of Robotics. The younger Amanda is sympathetic to him, and Andrew discovers he feels emotions, and is drawn to spend more time with his "Little Miss". He accidentally breaks one of her glass figurines and is able to carve a new one out of wood, which surprises her father Richard. Richard takes Andrew to NorthAm Robotics to inquire if Andrew's creativity was part of his programming. NorthAm's CEO Dennis Mansky claims this is a problem and offers to scrap Andrew, but instead Richard takes Andrew back home and encourages him to continue his creativity and explore other humanities. Andrew becomes a clockmaker and earns a sizable fortune managed by Richard after they find that robots have no rights under current laws.
Time passes, and Richard encourages Dennis to give Andrew the ability to present facial expressions to match his emotions. About two decades from being awoken, Andrew presents Richard with all the money he has made to ask for his freedom. Richard refuses to accept it but does grant Andrew his independence on the condition he may no longer reside at the Martin home. Andrew builds his own home by the beach. In 2048, Richard is on his death bed. He apologizes to Andrew for banishing him before he dies.
Following Richard's death, Andrew goes on a quest to find other NDR robots that are like him, frequently communicating back to Amanda, who has since married and divorced, and has a son Lloyd and granddaughter Portia. Ten years into Andrew's quest he discovers Galatea, an NDR robot that has been modified with female personality and traits. Andrew becomes interested in how Galatea was modified by Rupert Burns, the son of the original NDR designer, and finds he has a number of potential ideas to help make robots appear more human-like. Andrew agrees to fund Rupert's work and to be a test subject, and is soon given a human-like appearance. Ten years later, Andrew finally returns to the Martin home and finds that Amanda has grown old while Portia looks much like her grandmother did at her age. Portia is initially cautious of Andrew, but soon accepts him as part of the Martin family.
Amanda eventually dies, and Andrew realizes that all those he cares for will also pass on. He presents ideas to Rupert to create artificial organs that not only can be used in humans to prolong their lives but also to replace Andrew's mechanical workings. Andrew gains the ability to eat, feel emotions and sensations, and even have sexual relationships, resulting in him and Portia falling in love. Andrew petitions the World Congress to recognize him as a human as to allow him to marry Portia, but the body expresses concern that an immortal human will cause jealousy from others. Andrew returns to Rupert for one last operation: to change the artificial fluids driving his body into a blood equivalent. Rupert cautions him that the blood will not last forever, causing his body to age, and Andrew will die in several more decades, a fate Andrew accepts.
Decades later, Andrew again approaches the World Congress to appeal their past decision, wanting to be able to die with dignity. Later, with Andrew's body deteriorating, he and Portia are both under life support monitored by Galatea, now with a human appearance. They hold hands and watch the World Congress as they recognize Andrew as a human being, the world's oldest at two hundred years, and giving all rights confirmed by that, including validating his marriage to Portia. During the broadcast, Andrew passes away. Portia asserts that Andrew already knew the answer to whether he was human and then, after ordering Galatea to turn off her life support, she soon dies, hand-in-hand with Andrew.
- Robin Williams as Andrew Martin, an NDR android
- Sam Neill as Richard "Sir" Martin, the patriarch of the Martin family
- Embeth Davidtz as Amanda "Little Miss" Martin (adult) and Portia Charney
- Hallie Kate Eisenberg as Amanda "Little Miss" Martin (age 7)
- Wendy Crewson as Rachel "Ma´am" Martin
- Oliver Platt as Rupert Burns
- Kiersten Warren as Galatea, the NDR android servant of Rupert
- Stephen Root as Dennis Mansky
- Angela Landis as Grace "Miss" Martin (adult)
- Lindze Letherman as Grace "Miss" Martin (age 9)
- Bradley Whitford as Lloyd Charney (adult)
- Igor Hiller as Lloyd Charney (age 10)
- John Michael Higgins as Bill Feingold, Martin Family Attorney
- George D. Wallace as the President/Speaker of the World Congress
- Lynne Thigpen as Marjorie Bota, a later President/Speaker of the World Congress