British number two Watson made the main draw at Roland Garros, which begins on Sunday, in dominant fashion, brushing aside Anett Kontaveit of Estonia in straight sets.
The 22-year-old needed just 48 minutes to wrap up the 6-1 6-1 win on Saturday morning and continue her recent run of form following last week's Prague Open title.
"Winning is a habit they say," she said. "I'm just taking advantage of how much I'm enjoying it, fighting, being healthy and just using that every day to play the best I can."
She joins men's duo Murray - the seventh seed - and Ward, who also got through qualifying.
Watson was once world no. 39 but illness and injury ravaged her 2013 season and she is slowly working her way back to form and fitness.
Fellow Brit Johanna Konta missed out, losing 6-7, 7-5, 6-0 to Ukrainian Yuliya Beygelzimer.
British female no.1 Laura Robson is injured and misses the tournament in Paris.
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- Anett Kontaveit