The 23-year-old singer and actress announced the news on her website Sunday, also noting her one-year wedding anniversary.
"We are extremely happy and ready to start this new chapter of our lives."
Duff recently told Us Weekly that "we both love kids and we're really excited. ... It was a big deal for us because we had a year to be married."
Duff appeared on the big screen earlier this year in the independent drama "Bloodworth." Her last album was released in 2009.
Canadian-born Comrie, 30, plays hockey for the Pittsburgh Penguins.