Her first professional tournament they played in 1999. The biggest success of her career she succeeded in 2002 when she in the final of the WTA tournament in Brussels was able to prevail in two sets against the Spaniard Arantxa Sánchez Vicario itself. She also reached the finals in the same year of Budapest, but it lost to Martina Müller of Germany.
In the same year she was voted in the election for Swiss Sportsman of the Year for Best Newcomer. In April 2003, it reached number 45 their highest placing in the tennis world rankings.
Casanova was also a very good double player. In 2003, she reached with her French partner Marion Bartoli the semifinals of the U.S. Open and the semifinals of the tournament in Filderstadt and New Haven. In 2004, she starred opposite of Alicia Molik in the final of the tournament in Amelia Iceland and Eleni Daniilidou with the final in Antwerp.
At the age of 20 years finished Myriam Casanova her career. Their last match was in July 2005 in the playoffs Fed Cup, she defeated Tamira Paszek there the Austrian with 1:6 and 3:6.
In February 2007 she returned to Biberach an der Riss for a single game they lost, briefly on the ITF tour back. Myriam also tried again in 2009 to return to the tour. At the ITF tournament in Ismaingen she struggled through qualifying and was eliminated in the second round of.