This week's plenum was another step in that process, setting the tone for a party congress next year that will not only grant him five more years in power but will also elect those who will stand beside him on the seven-member Politburo Standing Committee.
It also appeared to back his campaign to clean up the party from within and battle corruption.
The term "core" leader was first coined by strongman Deng Xiaoping, who conferred it posthumously on Mao Zedong but also on himself and his effective successor Jiang Zemin. It is supposed to mean that their authority should not be questioned.
It was not a title that Xi's predecessor Hu Jintao was ever granted.
"Xi has achieved his minimum goal," said Ye Fei, a political analyst at China Policy, an analysis and advisory firm in Beijing. "His notional authority has been established. But how substantial it is has yet to be observed."
In the months to come, it will become more apparent whether Xi has also been successful in promoting loyalists within party ranks, paving the way for the 2017 congress, he said.
Xi's elevation to the "core leadership" was not a surprise. Indeed, in the weeks leading up to the plenum, state media issued a steady drumbeat of articles underlining the need for loyalty to the leader and to the party. China's people, it cited one poll as showing, are demanding strong central leadership under the "pioneering figure" of Xi Jinping.
But experts say that emphasis is revealing in itself, showing Xi's frustration at his inability to force through his agenda.
"China has a saying, that whatever you make a noise about is what you lack," said Zhou Xiaosheng, a sociology professor at Renmin University of China in Beijing. "It is obvious that all this noise about loyalty is because there is a lack of loyalty."
That is partly because of the scale of the task Xi has set himself: to clean up a deeply corrupt Communist Party whose moral atrophy threatens the very existence of the one-party state, and to stop the rot without bringing the whole structure crashing down around his ears.
Xi, experts say, has been facing growing resistance and resentment from within the party itself, coupled with an increasingly cynical public mood.
The Government announced on Monday that more than a million officials, out of 88 million party members, have been investigated in the past three years during an intense campaign against corruption.
State media has railed against lazy, foot-dragging officials, complaining that some were too scared of do their jobs for fear of being accused of taking bribes, while others were unwilling to act unless the kickbacks resumed.
And those who complain or are nostalgic for the good old days? Well, they are just "rotten with corruption", the People's Daily wrote.
Xi's signature anti-corruption campaign is both an attempt to clean house and restore public trust, and a tool to be used against opponents to scare them into submission.
But on both counts, it is also a double-edged sword: it has earned him many enemies within the party, experts say, and exposed to the general public just how deeply the cancer of corruption has penetrated.
"Xi is fighting on his own on a rotten stage," said Zhang Lifan, a historian and prominent critic of the president.
"He has hit and hurt everybody, he has insulted everyone. In their hearts they [party members] want to drag him down."
Nor has the anti-corruption campaign reassured the general public. Indeed, the constant drip of news about crooked officials may have had the opposite effect.
"People have become burned out," said Hu Xingdou, a governance expert at Beijing Institute of Technology. "They are not fools. They can see very clearly there are far more corrupt officials at large who have not been caught."
A poll released this month by Pew Global Research showed political corruption was the Chinese public's top concern: 49 per cent said corrupt officials were a very big problem - a rise of 5 percentage points from the year before. Another 34 per cent called it a moderately big problem.
The fact that the anti-corruption campaign's high-profile victims have been from rival factions within the party - and never from Xi's own inner circle - has not gone unnoticed.
"During the first year of the anti-corruption campaign, Xi Jinping was very popular," said Willy Wo-Lap Lam, a professor at the Chinese University of Hong Kong. "But after seeing the identities of the people he has pulled down - most of them were his political enemies - a groundswell of cynicism has set in."
Corruption had seemed manageable when the economy was booming: at least everyone was getting richer, even if some were doing it faster than others. But as growth has slowed, so distrust has grown, said Renmin University's Zhou.
"People are numb about the anti-corruption campaign now," he said. "They just think: 'Okay, you higher party people fight behind closed doors. We don't want to know. How corrupt you are has nothing to do with the common people.'"
In many ways, Xi faces a similar set of problems to former Soviet leader Mikhail Gorbachev in the 1980s, including a slowing economy and a corrupt, truculent party opposed to reform.
And the Soviet example is never far from his mind, experts say.
"The Soviet collapse teaches the CCP [Chinese Communist Party] lessons in party leadership," the nationalist Global Times tabloid reminded its readers this week, citing Su Wei, a professor at a Party School in Chongqing, stressing the need for greater discipline.
But while Gorbachev's policy of glasnost tried to harness openness and transparency to clean house, Xi has moved in the opposite direction, clamping down on the media, civil society and the legal profession.
Having seen Gorbachev lose control of the process, leading to the collapse of the Soviet Union, Xi has centralised power and tried to clean house from within.
"The new Long March for the party is about self-rectification and self-correcting," said Jude Blanchette, an expert in Chinese politics at the Conference Board in Beijing. "Self is an important word. This is about fixing ourselves."
But China Policy's Ye Fei said Chinese officials have been addicted to corruption for centuries, and much more powerful emperors than Xi have tried and failed to eradicate it.
"With the economy in deep trouble, there is not much an anti-corruption campaign can do to restore public patience with the status quo," he said. "That doesn't mean people will proactively take to the streets as the Egyptians did a few years ago, but they are voting with their feet - rushing to immigration agencies and putting their children in international schools."
