In January 2009, she won the inaugural HSBC LPGA Brasil Cup 2009, an unofficial LPGA event with a field of 14 LPGA players and a Brazilian national amateur. Matthew was five months pregnant with her second child at the time of the victory.
On 2 August 2009 at Royal Lytham & St Annes, Matthew won the Ricoh Women's British Open with a final score of 3-under-par over second-place finisher Karrie Webb. It was her first win in a major tournament. The victory came 11 weeks after she gave birth to her second daughter, Sophie. She was the first player from Scotland to win a women's major golf tournament.
In July 2009, Matthew and her husband escaped a fire at the hotel they were staying in while she played in the Evian Masters. Graeme suffered burns to his feet and was unable to caddy for two rounds.