Members of Parliament were back in Ottawa today after a week away from the House of Commons, and they returned with Thomas Mulcair as the new Official Opposition leader and with a federal budget looming.

Thursday's budget will be Mulcair's first major test in his new role after being elected to succeed the late Jack Layton as NDP leader on Saturday.

The economy and whether the government will use Thursday's budget to improve it was the topic of Mulcair's first questions in question period. He was given a standing ovation by all MPs and then asked why the government is failing to protect jobs.

Prime Minister Stephen Harper wasn't there to answer — he's on a trip in Asia — so Heritage Minister James Moore defended the government's management of the economy.

Mulcair asked whether the government will use Thursday's budget to give jobs and hope to young people; Moore said the budget will continue with the government's job-creation efforts.

The new leader told reporters after question period that it was emotional for him to be sitting in his friend Layton's seat.

The standing ovation from Conservative and Liberal MPs for Mulcair was preceded by Conservative MP Jeff Watson using his member statement to bash Mulcair and his party's policies. Watson said he has a "divisive personality" and "ruthless ambition," but Mulcair said his party will respond accordingly to how the government tries to define him and the NDP.

NDP will propose, not just oppose policies

"The best way for us to respond to that is by showing what our plan is. We're there of course as the Official Opposition, sometimes to call the government to account, to oppose, but more and more you're going to hear us propose," he said.

"People will have a clearer idea of what the NDP is putting on the table as we go through the next couple of years. They're very good at defining their adversaries, we're going to start to define them."

The government's budget on Thursday is expected to outline what changes it intends to make to Old Age Security and Mulcair said pension reform is going to be a priority issue for the NDP.

The Official Opposition's reaction to the budget doesn't carry as much weight in a majority Parliament as it does in a minority one, but how Mulcair handles it will still be important and is sure to be watched closely.

The NDP caucus insists it is coming back to Ottawa united and ready to take on Prime Minister Stephen Harper and the Conservatives, despite a long leadership race that had MPs dividing their loyalties among Mulcair and the other caucus candidates, Niki Ashton, Nathan Cullen, Paul Dewar and Peggy Nash.

Brian Topp, a backroom NDP strategist, finished second in the race and also had some MP endorsements, including from Libby Davies, the party's deputy leader, who will maintain that role, according to Mulcair. Martin Singh, a New Democrat from Nova Scotia, also ran and dropped off the ballot after the first round of voting.

The four defeated MP candidates also returned to Parliament Hill after being absent for much of the past few months while they travelled the country campaigning. They say they're looking forward to getting back to work and resuming their duties as MPs. They each made statements in the House of Commons ahead of question period to thank their families and campaign teams and said Mulcair has their full support.

Olivia Chow, Layton's wife and a Toronto MP, also made a statement, saying she's proud to have a leader that worked with her husband to unite Quebecers and Canadians.

"More than ever we are strong, we are united, so today, we continue Jack's legacy and rally behind our new leader, the leader of the Official Opposition and I couldn't be more proud," she said.

Nash was the party's finance critic but had to give up the role when she entered the leadership race. Peter Julian, caucus chair, was appointed to take her place. Nash said Sunday she doesn't know if she will resume the critic role, saying Mulcair hasn't made those decisions yet.

The party's finance critics play prominent roles leading up to a budget and in its aftermath. Thursday's budget is expected to be one ripe for criticism from the opposition parties because of the cuts that will be in it.

The NDP's newest MP, Craig Scott, was also on Parliament Hill on Monday, although he won't be taking his Commons seat  as the member for Toronto-Danforth just yet. He claimed victory in last Monday's byelection, held to fill the void left by Layton, but he can't be sworn in until Elections Canada declares the results official.

New Democrat Charlie Angus said the dynamic in the House will be different.

"Now we're coming back unified, we've got a great leader and all our leadership candidates are coming back, so we're ready to rock Stephen Harper's world," Angus said as he arrived on Parliament Hill. "You're going to see a really energized New Democratic caucus."

Another MP who has been absent for the last few months and is returning to work is Conservative MP Steven Fletcher. The Manitoba MP and junior cabinet minister is a quadriplegic and had major surgery to replace the titanium rod in his neck in January. Fletcher is the minister of state for transport.