David Miranda was held by police under terror laws for nine hours - the legal limit before a suspect must be charged or released - as he changed planes on a journey from Berlin to Brazil.
Labour has called for an urgent investigation into the use of the powers to question Mr Miranda, who lives with reporter Glenn Greenwald, the journalist who interviewed American whistleblower Edward Snowden.
Mr Miranda said: "There were six different agents. They asked questions about my entire life. They took my computer, video game, mobile phone, my memory card."
Mr Miranda was questioned under schedule 7 of the Terrorism Act 2000 which applies only at airports, ports and border areas, allowing officers question and detain individuals.
Shadow Home Secretary Yvette Cooper said: "Any suggestion that terror powers are being misused must be investigated urgently - the public support for these powers must not be endangered by a perception of misuse."
Downing Street said the case was an "operational matter for the police".
Bob Satchwell, executive director of the Society of Editors, said it was difficult to avoid the conclusion that the move was an attempt to intimidate a journalist.
Mr Greenwald said: "This is a profound attack on press freedoms and the news-gathering process. It is clearly intended to send a message of intimidation to those of us who have been reporting on the US National Security Agency and GCHQ."