In 1913 he founded the Manchester Press Agency. Collin's father William died only weeks before the outbreak of World War I, and his mother Isabella died shortly afterwards, on Christmas Eve 1915. Two weeks later Collin married Lillian Susanna Marsden, and they had four children: Barbara (who died in infancy); Rosemary Collin Brooks (1920–1971), whose career included a stint working for MI5; Vivian Collin Brooks (1922–2003) — a journalist who wrote a number of detective books under the pen-name "Osmington Mills"; William Austen Brooks (1924–1986), also a journalist: and Edward Clarke Brooks (1928–) who became an actor and wrote a number of short stories.
His own field notes — taken from his pocket book — of this event run as follows:
His war service was followed by an increased awareness and involvement in politics and journalism. In 1921 he was employed by the Liverpool Courier; in 1923 he joined the Yorkshire Post, and moved in 1928 to their London office. This was followed by a move to the Financial News later that year. In 1933 he moved to the Sunday Dispatch, which began his long involvement with Harold Sidney Harmsworth, 1st Viscount Rothermere. He was shortly elevated to the position of Editor of the Sunday Dispatch. (A fuller record of his career from 1932 to 1940 can be found in "Fleet Street, Press Barons and Politics" edited by N.J. Crowson, ISBN 0-521-66239-7).
With his work for Rothermere, the family spent time living both in London and also in Norfolk — in a house called "The Mount" on Rothermere's Stody estate.
He later worked on a number of other papers, being Chairman and Editor of "Truth" (an exposé magazine aimed at political and society issues) from 1940 to 1953, and wrote the "Letter to America" on a regular basis. He was also a ghost-writer for a number of people, and many political speeches and white papers were influenced to some extent by him.
He was a member of a number of clubs, including the Savage Club, and the book "Brother Savages and Guests" by Percy V. Bradshaw includes some illustrations by Brooks.
Collin Brooks was a prolific writer, with over fifty books to his name, from authoritative works on finance and legal cases, through literary novels under his pen-name "Barnaby Brook" and two volumes of poetry, to what he called his "shockers" — detective stories which introduced such delightful characters as Lord Tweed, Raeburn Steel, Dan'l Forray and his twin daughters Jo and Jack, Inspector "Doleful" Debenham,and the unforgettable Oswald Swete McTavish. A search on Amazon UK for "Collin Brooks" in "books" will still find a surprising number of his works — together with those of his daughter Vivian.
In addition to his published works he produced, throughout his life, his own Journals (edited extracts from which form the basis for N. J. Crowson's book mentioned above.) The Journals cover a period of some three decades, and run to millions of words. For much of the time he had three or more literary works — not including the Journals — "on the go" at any one time, which one he worked on on any given day depending on his mood.
His later career expanded from journalism into broadcasting, where he was a member of the original "Any Questions" team and also of "The Brains Trust", both for BBC Radio, and did a regular stint as "Northcountryman" on radio broadcasts.
He was a man with a vast circle of friends, acquaintances and correspondents from many walks of life; his letters appear in a surprising number of collections. T. S. Eliot, a family friend, gave an address at Collin Brooks' memorial service at St Bride's Church, Fleet Street, London in 1959.