Born in Colombo to Frederick Charles Loos, member of the Legislative Counci and Jane Harriet Keith, he was educated privately before studying at the City of London School, University College, London and Gonville and Caius College, Cambridge graduating in 1887 and was called to the bar as a barrister at the Inner Temple.
On his return to Ceylon he was admitted as an advocate of the Supreme Court and became private secretary to Justice Lovell Burchett Clarence.
He started his own practice in the unofficial bar in 1890, and joined the Attorney General's Department as Acting Office Assistant and Additional Crown Counsel.
[1] He was elected as an unofficial member in the 1921 legislative council election and was nominated in 1924 as an unofficial member by the Governor to the Legislative Council of Ceylon.
[2] The Hermann Loos Championship Trophy has been awarded annually since 1917 to the best performing cadet platoon of the National Cadet Corps at its annual camp at Diyathalawa.