MP Eric Joyce has been charged with three counts of common assault after an alleged fight in a House of Commons bar.
The 51-year-old MP for Falkirk had already been suspended by the Labour Party until the investigation was completed.
Staff at Strangers Bar who were on duty on Wednesday evening were later interviewed at Belgravia police station.
Officers have also interviewed MPs who were present during the alleged attack.
It is understood police were called to Strangers Bar in the Commons at about 11pm on Wednesday.
Commons Speaker John Bercow has asked MPs not to discuss the incident in the Chamber.
"Members will be aware of reports of a serious incident in the House," he said.
"I have been informed by the Serjeant at Arms that the honourable member for Falkirk has been detained in police custody.
"The matter is being investigated. I take this matter very seriously, as do the House authorities."
Mr Joyce, the MP for Falkirk since December 2000, served in the Army Education Corps before pursuing a career in politics.
