Colum Eastwood claimed the poll would be potentially decisive in a country divided over Brexit and facing extended industrial action by health workers disgruntled at pay levels and critical of the powersharing stalemate.
He said EU withdrawal was a massive roadblock in the way of future progress but his MPs would show up and try to block it in Parliament.
The party is in contention for seats in South Belfast and Foyle.
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Mr Eastwood said: "History doesn't judge those who don't turn up at defining moments - it casts a far harsher verdict.
"It simply doesn't mention them because they make no difference.
"You only make a difference by being there.
"Decisions are made by those who show up."
He said Sinn Fein had "abstained" from its responsibility to govern at Stormont and oppose the EU divorce at Westminster.
His Irish republican rivals do not take their seats in the House of Commons on principle.
The SDLP leader said: "In this election we simply can't afford the luxury of voicing a strong protest.
"Turning your back on Brexit and ignoring it won't prevent it from happening.
"Preventing it means facing it head on - it means voting against it.
"It means voting for people who will go to work and vote against it."
Sinn Fein leader Mary Lou McDonald has said it was a dishonest farce to assume that Irish MPs could make a difference to the British Government's Brexit strategy.
Mr Eastwood launched his party's General Election manifesto in Londonderry.
He said: "In Derry and across Northern Ireland, we also know that there lies the threat of a massive roadblock in the way of our future.
"The threat of Brexit and Boris Johnson looms over this election."
The SDLP leader is in a tight fight for the Foyle seat with Sinn Fein's Elisha McCallion.
He said: "We are launching this manifesto for change in Derry because this city is most in need of that change.
"Derry is tired of empty words and tired of empty seats.
"Derry deserves delivery."
Unionists have called for the British Government to appoint ministers to take key decisions.
Mr Eastwood said: "The current semi-skimmed direct rule could be very quickly replaced by the full fat Boris Johnson version if Stormont is not restored soon.
"This election is about Sinn Fein's empty seats and the DUP's empty promises.
"But it also has to be about an empty building in Stormont.
"Not one person in Northern Ireland has benefited from the stalemate in our politics."
He said for more than 1,000 days both the DUP and Sinn Fein had been abstaining from responsibility to deliver a government for all of our people.
"Hospital waiting lists have grown longer and longer because they have forced all of us to wait for nearly three years for a government."