Ho lat Seng, 44, took the oath with the blessing of Xi, who commended him for diversifying the city's economy and working toward greater integration with China during his stint as president of the region's legislative assembly between 2013-19, reports Efe news.
The swearing-in ceremony also celebrated the 20th anniversary to Macao's return to China from Portugal after having belonged to the small Mediterranean country for nearly four-and-a-half centuries.
Xi said Macao should take advantage of the opportunity presented by the Belt and Road Initiative and the Guangdong-Hong Kong-Macao Greater Bay Area project, referring to infrastructure plans that Beijing says will contribute to the development of the southern part of the country.
During the last 20 years, Macao has witnessed the most significant development in its history, Xi said, praising the way in which the special administrative region had effectively implemented the "One Country, Two Systems" formula that governs China's relations with Hong Kong and Macao.
Beijing holds sovereignty over the two island territories but allows them a certain amount of autonomy and freedoms, a system set to continue until 2047 (in the case of Hong Kong) and 2049 (Macao), 50 years after the end of their colonial status and return to China.
However, Xi added that the "One Country" principle was a prerequisite for the existence of "Two Systems", and that distorting this guiding principle may endanger the whole arrangement - a not-so-thinly-veiled warning directed at Hong Kong, where massive anti-Beijing protests have taken place for the past six months.
By establishing infrastructure such as the Hong Kong-Zhuhai-Macao Bridge, a macro-project that was completed in October 2018 after years of delays and cost overruns, China has tried to accelerate the former colonies' integration.
Xi's visit stoked significant controversy on Thursday after Macao banned the entry of at least six Hong Kong activists and journalists from three media groups who planned to attend the celebrations.
The local police said the Hong Kongers' activities could "endanger public order".
( With inputs from IANS )