Brazeau, who has weathered several controversies since his appointment in 2009, will continue to sit in the Senate as an Independent.
Police said Thursday charges have not yet been laid against a man arrested at Brazeau's home in Gatineau, Que., across the river from Ottawa, and the investigation is ongoing.
CBC News learned Brazeau was arrested at 9:10 a.m. ET Thursday at his residence after a call to 911.
If police choose to press charges, Brazeau would appear in court at 9 a.m. ET Friday, Const. Pierre Lanthier said. In Quebec, the Crown is responsible for laying charges.
"But for sure we, like I said, will object to his release and we will speak with the Crown attorney to see whether we have enough evidence to lay any charge," he said.
Lanthier did not use Brazeau's name, but sources confirmed to CBC News earlier in the day that it was Brazeau who had been arrested.
Lanthier spoke to reporters just before 4 p.m. ET. He there was a "strong possibility" that the house — a crime scene — would be searched soon.
"Listen, it's a little too early [to discuss possible charges]," Lanthier said. "We're talking about domestic violence, there's a lot of things that the investigators have to check on. They have to go meet the people, it's not over yet."
Brazeau was being questioned just before 5 p.m. ET, Lanthier told CBC News.
Brazeau kicked out of caucus
Marjory LeBreton, the government Senate leader, sent a letter to Brazeau's office and caucus members in the morning informing them of his removal.
"In light of the serious nature of the events reported today, Senator Brazeau has been removed from the Conservative caucus. As this is a legal matter, I cannot comment further," LeBreton said in a statement.
A senior government source said Prime Minister Stephen Harper was saddened and shocked by the latest Brazeau developments, and took action immediately.
In question period, Harper called the matter serious.
"Obviously, Mr. Speaker, I think our understanding is that these are matters of a personal nature rather than Senate business, but they are very serious, and we expect they will be dealt with through the courts."
Brazeau already under scrutiny
Brazeau was one of several senators who have come under scrutiny for claiming to live outside Ottawa while collecting a generous housing allowance.
Last November, a media report said Brazeau was claiming a Senate living allowance despite spending most of his time in the National Capital Region.
Senators can claim up to $21,000 a year if they live primarily more than 100 kilometres away from the Ottawa-Gatineau region. The report said Brazeau claimed he lived in Maniwaki, Que., but his primary residence is in Gatineau.
That report, along with reports that two other senators were claiming the allowance while already living in Ottawa, led the Senate to audit its members' primary residences. The Senate board of internal economy has had senators turn over proof of residence, including health cards, driver's licences and tax forms.
Brazeau said at the time that he was glad the Senate struck a subcommittee to look into the issue.
"I look forward to providing the facts that prove my primary residence is in Maniwaki, Que., contrary to what has been reported," he said in an email.
"I built my reputation on the need for greater accountability, and I will continue practising what I preach."
MP reaction mixed
Conservative MP Eve Adams, parliamentary secretary to the veterans affairs minister, said her caucus colleague will get due process.
"You are innocent until proven guilty, but if he has harmed a woman and beaten a woman, then I hope he receives the full brunt of our justice system," Adams said.
New Democrat MP Romeo Saganash declined to comment.
"I never commented on things like that and I won't start today. The man is down. The man is down," he said, shrugging.
New Democrat ethics critic Charlie Angus said his party was more concerned about the allegations of fraud than the allegations of domestic abuse.
"I really don't want to get into anything on the domestic abuse situation or whether it's true or not. I felt it unfortunate that the Conservatives are actually hiding behind that. The bigger issue for us is accountability. There's been allegations of him ripping off the taxpayer. There's been allegations of tax fraud," Angus said.
Known for boxing, verbal sparring
Among controversies Brazeau has been involved in include an episode last summer when he took to Twitter to insult a journalist, rhyming her name with a demeaning word.
The journalist had reported that Brazeau had the worst attendance record in the Senate.
Brazeau has been criticized for his frequently colourful language on social media. He fought now-Liberal leadership candidate Justin Trudeau in a charity boxing match last March and lost. He has a second-degree black belt in karate.
Brazeau has also reportedly fallen behind on child support payments several times, with the most recent report saying the Quebec government garnisheed his salary to get the money. Brazeau said he is up to date with what he was ordered to pay.
Before he was appointed to the Senate, Brazeau was the head of the Congress of Aboriginal Peoples, the national organization that represents off-reserve aboriginals.
Recently, Brazeau was a vocal critic of the Idle No More movement, and made disparaging remarks about Attawapiskat Chief Theresa Spence's recent hunger strike.