Maclean practised as a solicitor with practices in Cardiff and Lincoln's Inn Fields, London. A member of the Presbyterian Church of England, he was vice-president of the Cardiff Free Church Council in 1902–3, and also worked closely with the National Society for the Prevention of Cruelty to Children. He was a last-minute choice as one of the Liberal Party candidates in Bath at the 1900 general election, but was defeated at the polls. At the 1906 general election, he stood again and was elected as a Liberal Member of Parliament for the constituency. Whilst an MP he voted in favour of the 1908 Women's Enfranchisement Bill.