The 36-year-old actress gave up her acting career upon her engagement to Prince Harry.
Markle told the BBC in the couple's joint interview: "I don't see it as giving anything up. I just see it as a change. It's a new chapter."
For Heigl, 39, this could be her comeback moment.
"Joining 'Suits' was the perfect organic way to not only collaborate with an EP I admire deeply, but to also become part of a show and cast that I am an immense fan of," Heigl said in a statement from USA Network. "I have watched 'Suits' from the very beginning and feel incredibly lucky to be the newest member of the Pearson Specter Litt family."