Jan Scheuermann, who is 53 and paralysed from the neck down, was able to deftly grasp and move a variety of objects just like a normal arm.
Brain implants were used to control the robotic arm, in the study reported in the Lancet medical journal.
Experts in the field said it was an “unprecedented performance” and a “remarkable achievement”.
Jan was diagnosed with spinocerebellar degeneration 13 years ago and progressively lost control of her body. She is now unable to move her arms or legs.
She was implanted with two sensors – each four millimetres by four millimetres – in the motor cortex of her brain.
A hundred tiny needles on each sensor pick up the electrical activity from about 200 individual brain cells.