Stephen Harper will resign as the MP for Calgary Heritage before Parliament resumes in the fall, as he pursues new interests on corporate boards and the establishment of a foreign policy institute, according to close confidants of the former Conservative prime minister.

Mr. Harper has not decided whether to resign as an MP when Parliament adjourns at the end of June or during the summer months, but friends say he won't be back in the Commons in September.

"He is not going to be there when the House returns in September," one close associate said. "He has had some good conversations about what is next for him. … He has some board discussions happening and he's looking at some options about setting up his own institute."

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The institute is in its early stages of discussion, but friends say it won't be academic or domestic-policy focused, such as the conservative think tank founded by former Reform Party leader Preston Manning. Mr. Harper's interests will be directed largely at global "big picture" issues that he has espoused over the years.

Mr. Harper is deciding on his future as the Conservatives get set to honour a leader who served as prime minister from February, 2006, until his defeat in last fall's federal election. He is scheduled to be feted at a Conservative policy convention in Vancouver on Thursday night.

His former policy director, Rachel Curran, said once Mr. Harper leaves politics, he will want to champion global free trade, building on his success in negotiating deals with South Korea and the European Union, as well as the Trans-Pacific Partnership.

"He spent tremendous time and energy really concluding these trade agreements and opening up trade corridors," Ms. Curran said. "He has got a really recognized expertise and a lot of respect internationally in terms of his kind of knowledge."

She said Mr. Harper will also want to promote his geopolitical thinking – whether it's on human rights, the promotion of democracy or standing up to authoritarian regimes.

Mr. Harper was a strong defender of Israel and a harsh critic of Iran. His government severed diplomatic relations with Tehran, a policy the Liberal government says it will reverse. He also helped marshal Western efforts to impose sanctions against Russia over President Vladimir Putin's annexation of Crimea and intrusion into eastern Ukraine.

"That is what we called his principled foreign policy. It recognized that we have to stay engaged with actors who don't behave very well because of their importance and size, but it doesn't mean we don't speak out about what we see as issues and problems," Ms. Curran said. "He will continue to speak out on those issues."

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Along with German Chancellor Angela Merkel, Mr. Harper pushed austerity and balanced budgets at the G20 summits, a view not shared by Prime Minister Justin Trudeau, whose government expects to run a $30-billion deficit this fiscal year.

"We really had the lowest federal tax burden in 50 years, which was where he was at the end of his mandate," Ms. Curran said. "He reduced the size and scope of federal spending, designing a successful Conservative stimulative program and then balancing the budget and doing regulatory reforms."

Since the Conservative government was defeated in last October's election, Mr. Harper has kept a low profile and avoided the national media, entering and departing from several back entrances in Parliament's Centre Block. He has not spoken in the House of Commons but has shown up for many votes.

"He will be very reluctant to get involved in domestic issues and speak out on those. He has a long record of accomplishment on that front, so I think he will move forward and not stay involved on those kinds of issues," Ms. Curran said.

So far, Mr. Harper has avoided saying anything on the record about the new Liberal government and its agenda of rolling back Conservative initiatives – from re-engagement with Iran and Russia, rescinding Tory tax breaks, bringing back the long-form census and promising to end minimum sentences.

Mr. Harper has no plans to leave Calgary, where he owns a home and where his daughter, Rachel, is enrolled in school. His son, Ben, is studying at Queen's University in Kingston.

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He recently attended an event at the Las Vegas home of casino owner Sheldon Adelson, who was hosting a meeting of the Republican Jewish Coalition. Mr. Harper's office said he attended "exclusively as an expression of his continuing support for Israel."