Respect's George Galloway has taken his seat in the House of Commons as the new MP for Bradford West.
He was officially sworn in on Monday - more than two weeks after his victory in a by-election - after Parliament returned from its Easter recess.
The one-time Labour MP captured the seat - previously held by his old party - with a majority of more than 10,000.
He has vowed to speak out about Bradford's economic problems as well as his opposition to the Afghanistan war.
After reading the traditional oath of allegiance to The Queen, Mr Galloway was offered his congratulations by MPs - including Education Secretary Michael Gove - and shook the hand of Speaker John Bercow.
Mr Galloway was a Labour MP between 1987 and 2003, until he was expelled from the party for comments he made about the Iraq war.
After co-founding the Respect Party, he won the seat of Bethnal Green and Bow at the 2005 general election. He failed to be re-elected to Parliament when contesting a different seat in 2010.
Mr Galloway earlier told the BBC's Daily Politics that he was pleased to be back in Parliament after an absence of two years and would be focusing on local matters, such as reducing youth unemployment in Bradford and regenerating the city centre.
"The first thing I have done is draw attention to Bradford's problems and I will be responsible for projecting solutions to these problems."
But he said he would also raise foreign policy issues as they were not "easily separable" from domestic matters.
"I don't think it is either, or. One of the reasons I won such a landslide majority is that because the other three parties have such an iron-clad consensus in support of the war in Afghanistan," he said.
"We said the war in Afghanistan should end right now and our soldiers brought back".