Chinese leader Xi Jinping cast himself as the decisive helmsman his country needs in surmounting great adversity, pledging to build a more secure, powerful and egalitarian nation as he signaled plans to extend his decadelong rule.

In a Sunday speech, opening a Communist Party congress where he is set to defy recent norms and claim a third term as party chief, Mr. Xi issued a robust defense of his record, shaking off concerns over Covid-19, a sluggish economy and troubled ties with the U.S. He recalled his efforts to curb corruption, rally public support for the party and champion China’s political system as a counterweight to Western liberal democracy.

A campaign of “self-revolution,” marked by forceful crackdowns on corruption and political dissent, Mr. Xi said, has “ensured that the party will never change in quality, change its color, or change its flavor”—party parlance for threats to Communist rule in China.