Del Mastro, a former parliamentary secretary to Prime Minister Stephen Harper, was convicted of exceeding spending limits during the 2008 election, as well as failing to report a personal contribution of $21,000 to his own campaign and knowingly submitting a falsified document.
"I hope someday to be back in this place, but if I don't, always keep in mind it's a simple chair, but it represents the hopes and dreams and futures of thousands you represent and millions across the country," Del Mastro told the Commons, his voice quavering as he glanced back at his seat.
"Never take it for granted."
Del Mastro had many friends within his former Conservative caucus, many of whom were among the colleagues who applauded his speech when he was finished, along with several opposition members.
He made it clear he was stepping down in order to prevent embarrassment and division within the Conservative ranks. On Tuesday, MPs debated for three hours whether to suspend him without pay; the government and the NDP was prepared to do so, but the Liberals wanted him expelled immediately.
"To my colleagues in the Conservative party, I told a number of you I would never put you in a position where you'd have to vote on my future," he said.
"Stay united. I will not divide you, I will not be the one that divides you. I believe too much in what you do and what we stand for."
The Prime Minister's Office responded with a short statement. "We wish Mr. Del Mastro and his family well," spokesman Stephen Lecce said in an email.
Del Mastro is the fifth Conservative parliamentarian to resign or face suspension since the 2011 election. Last year, three former Conservative senators were suspended over contested living and housing expenses, while former cabinet minister Peter Penashue resigned last year over improper campaign contributions.
Del Mastro was expelled from the Conservative caucus on the day he was charged in September 2013, and had been sitting as an Independent.
Del Mastro, whose wife gave birth to their first child — a girl — on Sunday, has said his lawyer has asked a judge to re-open his defence in order to introduce new evidence before sentencing, which is scheduled for Nov. 21.
During Wednesday's 15-minute speech, Del Mastro continued to maintain his innocence. In 2008, his supporters didn't vote for him based on automatic phone calls telling them to do so, he argued — a service that was at the heart of his trial.
"I was built with a design flaw: I wasn't built with a reverse gear, I only know how to go forward," he said.
Del Mastro's seat is one of three that are currently open in the House of Commons.