Did all actors and actresses do their own singing in Mamma Mia?

No, not all actors and actresses did their own singing in Mamma Mia. While some of the cast members, including Meryl Streep, Amanda Seyfried, and Dominic Cooper, did perform their own songs, others had their singing voices dubbed by professional singers. For example, Pierce Brosnan's singing was dubbed by British singer/songwriter Benny Andersson, and Colin Firth's singing was dubbed by Swedish singer/songwriter Björn Ulvaeus.