Qin's absence had sparked a storm of speculation that the 57-year-old, considered a confidant of President Xi Jinping, had fallen from grace or was subject to an official investigation.
China's foreign ministry had previously said "health reasons" were to blame but more recently had refused to give any updates despite repeated questioning.
State media outlet Xinhua said on Tuesday evening that China's top legislature had voted to remove Qin from office and replace him with his boss Wang Yi.
Xinhua did not give a reason for Qin's removal but said Xi had signed a presidential order to enact the decision.
Asked repeatedly about Qin earlier on Tuesday, foreign ministry spokeswoman Mao Ning told journalists that she had "no information" to offer and insisted that "China's diplomatic activities are steadily moving forward".
Rumour Mill In Overdrive
China has remained tight-lipped for weeks about the fate of Qin, who has not been seen in public since June 25 when he met Russia's deputy foreign minister Andrey Rudenko in Beijing.
His absence from a high-level ASEAN summit in Indonesia two weeks later first raised eyebrows, with Qin's health given then as the reason.
However, that did little to stem an explosion of rumours online, some of which claimed Qin was under official investigation for an alleged affair with a prominent television anchor.
"The CCP system is so opaque that it nurtured the rumours," Moritz Rudolf from Yale's Paul Tsai China Center told AFP.
On Tuesday, some analysts urged caution about jumping to conclusions.
"He keeps his more senior position as a state councillor," tweeted Neil Thomas from the Asia Society Policy Institute, a US think tank.
"So not 100 percent sure this is a purge."
Manoj Kewalramani, a China expert at the Takshashila Institution in Bengaluru in India, told AFP that Qin keeping the State Council role "could be a product of his proximity to Xi Jinping".
"It could be also a sign that this was not a product of displeasure with his work or any disciplinary violation but rather a health issue which prevents him from carrying out the intense (foreign minister) role," he said.
The Lowy Institute's Richard McGregor tweeted that the lack of information around Qin's disappearance was "a transparent example of the utter opacity of Chinese elite politics".
Many of Qin's duties over the past month had been taken on by Wang, China's top diplomat who leads the ruling Communist Party's foreign policy and outranks Qin in the government hierarchy.
Qin had only taken over from Wang as foreign minister in December last year.
"Rather than bring in someone new, you've got Wang Yi," said Kewalramani. "So you have somebody who's experienced... and can continue at least for the near future in that role."
Thomas noted that, because Wang now had two jobs, the situation "could be a temporary arrangement".
"Wang Yi is a veteran of China's diplomacy, and he is greatly trusted by the whole country," tweeted Hu Xijin, a prominent commentator with the Global Times state tabloid.
Both Qin's removal and Wang's appointment were trending on social media platform Weibo on Tuesday evening.
Qin's absence over the past month had left a vacuum at the top of China's foreign ministry.
A visit to Beijing by the European Union's foreign policy chief Josep Borrell was abruptly called off this month.
And Bloomberg reported on Friday that a visit by UK Foreign Secretary James Cleverly was also postponed due to Qin's situation.
"The whole situation makes the Chinese Ministry of Foreign Affairs and Beijing's diplomatic efforts look weaker than Beijing would like it to do," said Yale's Rudolf.
Originally from the northeastern city of Tianjin, Qin frequently rubbed shoulders with Xi in an earlier role as chief of the foreign ministry's protocol department.
His promotion over more experienced candidates, first to US ambassador and then China's number 2 diplomat, was attributed to the trust placed in him by Xi directly.
"The quick rise of Qin Gang might have created some resentment among other senior people within the Chinese Ministry of Foreign Affairs," said Rudolf.
A fluent English speaker, Qin was a visible presence in Washington through public and media appearances in which he defended the Chinese geopolitical position.
He also previously served as a spokesperson for the Chinese foreign ministry, where he gained a reputation for caustic responses to difficult questions from journalists.