Macmillan was born in Edinburgh in 1882. After an education at St Andrews and Edinburgh
University, she became a lawyer.
In 1908 she became the first woman to plead before the House of Lords when she advocated
that women graduates should be given the vote. Over the next few years she appeared before
several committees of enquiry on matters of concern to women including those on street
offences and unemployment insurance. Macmillan was also involved in the campaign against
the law that resulted in women losing their citizenship when they married a foreigner.
On the outbreak of the First World War Macmillan organised held for Belgian refugees.
Active in the attempts to obtain a negotiated peace, Macmillan was an organizer of the
Women Peace Conference at the Hague and was secretary of the International Women Suffrage
Alliance (1913-1920). After the
Armistice Macmillan was a delegate at the Paris Peace Conference.
Called to the Bar in 1924, Macmillan unsuccessfully stood as a Liberal for North Edinburgh
in the 1935 General Election. Chrystal Macmillan died in 1937.