Before a stand-in from his office literally stood in for the mayor while he conducted official business.

在他的办公室里有一个替身，意思就是在市长处理公务时代替他。

youdao

I stayed in Beijing for two days when I was on my official business.

我公出时，在北京耽搁了两天。

《新英汉大辞典》

Mandelson is in Paris on Tuesday morning on official business.

星期二的上午，曼德尔森由于公务到达巴黎。

youdao

Ney's office also says he had official business, too, visiting members of the Scottish parliament.

NPR: Scrutiny Falls on Those Close to Lobbyist

Bush's other brother, Florida Governor Jeb Bush, stayed home to tend to official business.

CNN: For Bush, a family affair in New Hampshire

In theory, the president is entitled to use it at taxpayers' expense only when he is on official business.

ECONOMIST: Lexington