Pictures and private details of John Sawers, who will take on the post in November, were revealed on an easily accessible profile page of his wife, Lady Shelley Sawers.
The page was taken down after the Mail on Sunday informed the Foreign Office. The Liberal Democrats called for an inquiry, while senior Tory MP Patrick Mercer said Sawyers had left himself open to blackmail.
But Miliband denied that national security had been compromised, saying it was “no state secret” that the MI6 chief wore Speedos on holiday.
Shadow business secretary Ken Clarke dismissed the potential security implications, saying Britain’s enemies “did not wholly rely on the Mail on Sunday and Facebook for their information”.
Sawers’s wife disclosed details, including the location of the London flat used by the couple and the whereabouts of their three children and of her husband’s parents.
She put no privacy protection on her account, allowing any of Facebook’s 200 million users in the open-access “London” network to see the entries.
Miliband told BBC1’s Andrew Marr Show: “What are you leading the news with that ... the fact that there’s a picture that the head of the MI6 goes swimming. Wow, that really is exciting.
“This allegation that there’s great secrets and then you find out it’s about his swimming trunks and the fact that his family’s getting dragged into it.”