The bill in the final reading was supported by 202 parliamentarians, 141 opposed and two more abstained from voting.
An adult citizen of Spain or a person with a residence permit in the country, suffering from an incurable disease and experiencing "unbearable physical or mental suffering" can request euthanasia.
Euthanasia is legal in Belgium, Luxembourg and the Netherlands.
In late January, the Portuguese parliament approved a bill to legalize euthanasia.