A lower court had acquitted Nicolas Bonnemaison last year in an emotionally charged trial that gripped a country where euthanasia is illegal.
The appeal court in the western city of Angers found Bonnemaison, 54, guilty of deliberately killing one of the seven, an 86-year-old woman.
Bonnemaison, his head lowered, did not react as the verdict was read out on Saturday.
The public prosecutor had sought a five-year suspended sentence. Bonnemaison had faced a maximum of life imprisonment.
The acquittal came just a day after France's highest administrative court authorised ending the life of a quadriplegic in a vegetative state, a landmark decision that divided his family and was immediately blocked by the European Court of Human Rights pending a review of the case.
Bonnemaison, who has been struck off the medical register, was accused of "poisoning particularly vulnerable people" -- five women and two men who died between March 2010 and July 2011 soon after being admitted to the hospital in the southwestern city of Bayonne where he worked.
Euthanasia remains illegal in France despite recent efforts to ease legislation dealing with the terminally ill -- a campaign promise by President Francois Hollande.
In March, lawmakers voted overwhelmingly in favour of a law allowing medics to place terminally ill patients in a deep sleep until they die.