The 32-year-old is leaving politics for a private-sector job and more family time.
Soudas was a Harper aide and adviser for nine years.
In recent years, he acted as communications director and sparred regularly with journalists over access and control of information.
He was the point man in a protracted effort to force journalists to sign onto a predetermined list of those allowed to question Harper during news conferences.
In his final briefing with members of the Parliamentary Press Gallery he said he'll miss a job which provided him with constant adrenaline.
Soudas began his career in municipal politics in his home town of Montreal.
In 2002, he came to Ottawa, joining Harper, who was then leader of the Canadian Alliance on the opposition benches.
He slipped into Harper's innermost circles, although he was rarely in the public eye. When he was caught by the cameras, he was the dark-haired fellow with the black, horn-rimmed glasses usually off to one side.
Soudas was seen as a loyalist fiercely devoted to the PM — in his farewell he called Harper "the best prime minister Canada has ever had." He was always seen as a man ready to run roughshod over anyone in defence of his boss.
His Blackberry never seemed to stop. He would bombard journalists with quotes, advice, criticism and complaints into the wee hours.
"I do, after all, have the responsibility to correct each and every media story that has been filed on the web, television, wire, print, even on Twitter because they contain errors that I simply had to politely, calmly and charmingly correct in order to ensure that they didn't lose any of the credibility they had with their readers," he said at his farewell briefing, perhaps with tongue in cheek.
As a key adviser on Quebec, he ruffled feathers among senior cabinet ministers leery of his unfettered access to the PM.
Some in the party were ready to turn on him when Tory political momentum in Quebec stalled, but Harper was loyal in turn to his aide.
Soudas initially announced his departure at a Tory caucus meeting in June.
As he wound up his last week, he told reporters he wants more time with his wife and three children.
"I spent more time with you guys than my own family, with my own kids," he said.
"I'll be able to take my daughter Georgia to her first day of school and that is another first I would surely have missed."