PM Modi wrote on his account on Chinese Twitter equivalent Sina Weibo, where he has around 1.85 lakh followers.
Modi's message of congratulations comes in the wake of a difficult period in bilateral ties, following the 72-day border stand-off in Doklam which ended on August 28. Modi and Xi had a cordial meeting in Xiamen, China, following the BRICS Summit in early September, with both having what officials described as "a forward looking conversation".
This followed their July 7 meeting in Hamburg at the G20, which officials saw as a turning point in pushing both sides to resolve the border stand-off peacefully.
At the Party Congress, which ended on October 24, Xi's status in the party was elevated with his name and ideological contribution, called Xi Jinping Thought, enshrined into the Party Constitution.
A new leadership line-up was unveiled on Wednesday, with Xi beginning his second-term without a designated successor and with many key allies in both the Politburo and the PLA Central Military Commission.