Callan wrote a series of British television adaptation novels of differing genres, including Capital City (ITV), Target: The Bronze Heist (Target), Sweet Sixteen and Jockey School (all BBC), and the novel Lovers and Dancers, set in Ireland during the famine.

In 2002, Callan published Did You Miss Me?, a novel exploring difficult female themes which was issued in a revised version in 2014.

[6][7] Callan has written biographies of Sean Connery, Anthony Hopkins, and longtime friend Richard Harris.

For fifteen years from the mid-nineties, Callan travelled throughout the United States interviewing more than 300 sources for Robert Redford: The Biography (Knopf, 2011).

The book was written with the co-operation of Redford, who traveled to Ireland to work with Callan and provided access to his diaries, scripts and personal records.

He adapted The Dead Secret by Wilkie Collins and Scales of Justice by Dame Ngaio Marsh for RTÉ Radio, and wrote the original plays The Train and Tripp.

He contributed more than 20 plays to the Dan Treston-produced series Treasure House, dramatising the lives of scientists and artists from Johannes Kepler to Edgar Allan Poe and H. G.

"[11] Subsequently, Callan joined BBC television drama in London, where he story-edited the detective series Shoestring.

[10] Collaborating with Anthony Shaffer, Callan was commissioned in 1987 by HBO to write The Negotiator, based on a treatment by Forsyth.

The Children of January, incidentally, refers to renegade outcasts of a dawning "parallel universe" civilisation that was abandoned.In 2011, Callan wrote and produced Channel 4's Sounds from the Cities.

Joining Morgan O'Sullivan's pioneering production set-up, Tara Productions, Callan collaborated in a strategy to acquire the defunct National Film Studios (as Ardmore Studios was then named), alter film investment law and attract Hollywood-based co-production into Ireland.

His directorial debut was with the six-part series My Riviera, in which Roger Moore, James Coburn, Sylvia Kristel, Charles Aznavour and Joan Collins reviewed personal favourite places along the Côte d'Azur, an area Callan has frequented since the 1980s.

He then made the documentary Back to Enchantment, about animators Gary Goldman and Don Bluth (An American Tail, Anastasia), which tied in with the release of Warner Bros' Thumbelina.

After a decade working on the Redford project, in 2005 Callan resumed directing with the film Luke Kelly: The Performer, which topped DVD charts in Ireland for eight weeks, achieving platinum sales status.

As part of its creative incentive scheme, in July 2011 Callan wrote and directed the two-day Magical History Tour event in Liverpool, culminating with a 7-hour live session from the Cavern Club streamed on YouTube.

[17][18] Also in 2011, he produced and directed the start-up episodes of The 2UBE Live from LIPA (the Liverpool Institute for the Performing Arts), a student production that was streamed on YouTube.

[19] Callan's art, in watercolour, oils and bronze sculpture, has been exhibited by the Blue Leaf Gallery in Dublin.

Irish Times art critic Aidan Dunne described his work as "a love affair with French painting", reflecting Callan's interest in L'École de Nice.

[26] In 2022 he won the Prix Littéraire Lucien Barrière, awarded by the jury of the Deauville American Film Festival for his non-fiction book, Robert Redford: The Biography.