The deal -- agreed to during the Winter Meetings -- was made official once the left-hander passed a physical on Friday.
Rowland-Smith, 27, has spent the previous four seasons with the Seattle Mariners, going 12-17 with a 4.57 ERA in 115 games, including 47 starts. He'll come to Spring Training competing for the fifth spot in the Astros' starting rotation.
The native of Australia posted solid numbers in 2008 and '09 but suffered through a 1-10 season with a 6.75 ERA in '10 before the Mariners non-tendered him. He pitched for Australia in the '04 Olympics and '06 World Baseball Classic.
Brian McTaggart is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.