Born in Rome, the daughter of a lithographer and a housewife, Ronchi graduated in historical and archaeological sciences and studied acting at the Accademia Nazionale di Arte Drammatica Silvio D'Amico. She started her career on stage, in which she worked with Fausto Paravidino, Carlo Cecchi and Valerio Binasco, among others. She made her film debut in 2010, in the drama La città invisibile.

In 2023, for her performance in the 2022 film Settembre , Ronchi won the David di Donatello for best actress. The same year, she was awarded the Nastro d'Argento for best actress for her performance in Marco Bellocchio's Kidnapped, and received a nomination for best actress at the Czech Lion Awards for her role in Il Boemo.