However, it's not clear whether the two were suspected of having a role in the girl's disappearance. Spanish television news reports on Thursday said the man may have tried to extort money from McCann's parents, offering information about their daughter's whereabouts, though police did not confirm that.
The man was detained on an international arrest warrant originating in France, a police spokeswoman said. She said the warrant itself had nothing to do with the McCann case, but would not elaborate or say what made police suspect him in the missing girl case.
The woman was detained due to her association with the man, and there was no warrant for her arrest, the spokeswoman said. She did not identify either suspect by name, saying the investigation was ongoing.
The man and woman both were arrested Thursday morning in Sotogrande, a town in the southern Spanish province of Cadiz, the spokeswoman said, speaking on condition of anonymity in line with police rules.
Members of the McCann family in Britain said they were withholding comment until more information was known.
"We have no comment to make, because we know no more than we have seen on the news," said John McCann, brother of Madeleine's father, Gerry.
Madeleine's great uncle, Brian Kennedy, said he did not know any details about the man's detention. "We are trying not to get our hopes up too much because they so frequently get dashed," he told Sky News.
Madeleine disappeared on May 3 after her parents left her and her brother and sister, 2-year-old twins, alone in their room while they went to a restaurant inside their hotel complex in Praia da Luz, a tiny resort town in Portugal's Algarve region.
Police have identified just one suspect in the case, but made no arrests before Thursday.
A month ago, Portuguese police said they were searching for a suspect — a white man between 35 and 40 years old — in connection with the girl's disappearance. They said the suspect had been wearing a dark jacket and beige trousers on the day the girl disappeared, and was spotted possibly carrying the girl near to where she had vanished.
Police have received countless tip-offs in the last two months, and the girl's parents have launched an international campaign to find her, enlisting the aid of celebrities such as soccer star David Beckham and J.K. Rowling, author of the Harry Potter books.