"These are very significant changes that are being made," Prentice told a news conference at Government House.
"This is new leadership in terms of how Alberta is represented."
Merrifield has resigned his federal seat in the Alberta riding of Yellowhead to move to Washington, D.C., to head up Alberta's trade relations with the United States.
Jay Hill, a former Conservative MP from British Columbia, will do the same for Western Canada and the North.
Career diplomat Ron Hoffmann will be Alberta's point person in Asia and is to immediately review the efficiency of Alberta's trade offices in the Pacific Basin.
Prentice said that Mar, Alberta's Hong Kong-based trade representative, will not have his contract renewed when it expires next June.
"(Mar) will work together with Mr. Hoffmann in the meantime to ensure that there's a seamless transition," said Prentice.
Mar, a former cabinet minister in the Ralph Klein era, had been the favourite to replace former premier Ed Stelmach when Redford came from behind to defeat him in the Progressive Conservative party's 2011 leadership race.
Redford appointed Mar to Hong Kong in what was later revealed to be one of the most lucrative jobs in Alberta's public service, with cash and benefits exceeding $500,000 a year.
Mar's salary, along with revelations of other lavish perks for Redford and her inner circle, became symbols of government entitlement and excess.
Redford quit the premier's job in March, amid plummeting poll numbers and ahead of a reported caucus and party revolt.
When asked if the Redford controversy played a role in Mar's departure, Prentice said, "Mr. Mar has worked very hard. He's done a good job on behalf of the people of Alberta.
"This is, however, time for a new government. It's time for a fresh start."
Earlier this month, Prentice won another Tory party leadership race to take over as premier. He promised that under his watch, jobs will be handed out on merit and not through personal connections.
Opposition critics said Prentice has already broken that promise by hiring Hill, who helped run the campaign for his successful leadership bid.
Merrifield spoke up to endorse Prentice's candidacy during the leadership campaign.
"Three days into the job, Mr. Prentice is already breaking key promises from his election campaign, awarding his closest friends and political insiders high-level positions in the Alberta government without even opening a competitive application process," Wildrose Leader Danielle Smith said in a news release.
"Actions speak louder than words, and welcoming one of his buddies into the PC Old Boys' Club is one of Mr. Prentice's first actions as premier,” noted NDP critic Deron Bilous.
Prentice defended Hill, saying he has shut down a private business to take on the job for 18 months at an "appropriate" salary level and will receive no severance.
He also noted that Merrifield and Hill will donate to charity the commensurate portions of their MP pensions while they work for the province, to allay any concerns about double dipping.
"I trust to the judgment of Albertans. If the opposition wants to be angry about that, I'm sure they will," said Prentice.