BRUSSELS—The European Union’s new leadership team has set a priority of deepening economic ties with China while protecting its own markets, a top official said, casting 2020 as a test of whether strains in Europe’s relations with Beijing can be reversed.

In an interview with The Wall Street Journal on Thursday, European Council President Charles Michel said he would lobby the bloc’s national leaders early in the new year on a more unified approach to Beijing, noting that past European efforts had lacked focus. He said while...