The "Jessica Jones" star debuted her baby bump as she arrived at the Academy Awards with Adam Granduciel.
Ritter, 37, wore a burgundy and nude lace gown with her dark hair in soft waves and a dark red lip.
She had a matching burgundy clutch.
The actress and the War on Drugs singer, 40, have been an item since 2015.
Ritter is a presenter at Sunday's ceremony.
Last week, Netflix announced that Ritter's hit Marvel series, "Jessica Jones," was canceled.
Ritter's rep did not immediately return a request for comment on the happy news.