Ur was educated at the Strathroy Middlesex General Hospital, receiving certification as a registered nurse assistant in 1964. She practised in this field from 1963 to 1966, then left to work as a farmer until 1990. She was first elected to parliament in the 1993 federal election, defeating her nearest opponent by almost 11,000 votes in the old riding of Lambton—Middlesex.
She was re-elected by similarly large pluralities in Lambton—Kent—Middlesex in the elections of 1997 and 2000.
Ur faced a difficult re-election in the federal election of 2004, defeating Bev Shipley of the newly formed Conservative Party of Canada by only 164 votes. Shipley could have requested a recount, but declined.
She was also an opponent of the federal gun registry, and sought to eliminate the program in late 2004. Ur was never appointed as a parliamentary secretary.
In the spring of 2005, Rose-Marie announced that she would not seek re-election in the 2006 federal election.