On July 1, 2008, Auld signed a two-year, $2 million deal with the Ottawa Senators as an unrestricted free agent. He came within one second of recording a shutout in his Senators debut against the Pittsburgh Penguins in Stockholm, Sweden, surrendering a powerplay goal in the final moments of the game. Though Senators' management expected him to serve primarily as a backup to Martin Gerber, Auld's strong play combined with Gerber's struggles resulted in Auld assuming the starting position early in the season. As the season progressed, Gerber was placed on waivers and ultimately was claimed by the Toronto Maple Leafs, while rookie Brian Elliott would split the goaltending duties with Auld in Ottawa. He was expected to challenge for the starting position in 2009–10 with Pascal Leclaire, acquired by Ottawa from the Columbus Blue Jackets late at the 2008–09 trade deadline, but was traded in the off-season on July 8, 2009, to the Dallas Stars in exchange for a sixth-round draft pick in 2010.