1986

History of the Doctor Who Universe
By this year International Space Command had regular Lunar flights and maintained a tracking station in Antarctica (DW: The Tenth Planet)

January

 * 04 - Earth writer Christopher Isherwood dies. He and Jack Harkness had once had a relationship. (TW: Reset)

April

 * 26 - Chernobyl goes into meltdown. (DWM: Black Destiny)

December

 * Humans first detect the Planet Mondas returning to the solar system, while it apparently was in orbit between Mars and Venus. The manned atmospheric probe Zeus IV is destroyed by the Cybermen inhabitants, and they go on to launch an attack on the Earth, starting with the Snowcap base in Antarctica. They plan to use a Z-bomb located here to destroy the Earth as one of their two worlds needed to be destroyed to save the other, but when they fail, Mondas is destroyed instead. Present for these events is the Doctor, and while the Cybermen are defeated, the strain of the conflict leads to his subsequent regeneration from his first incarnation into his second. (DW: The Tenth Planet)

Unknown date

 * Pete Tyler and Jackie Tyler marry. The event is witnessed secretly by their future daughter Rose Tyler and the Doctor. (DW: Father's Day)
 * Approximate year of the events of Harry Sullivan's War. Based upon the book's publishing date, coupled with statements that it takes place 10 years after The Android Invasion, established as taking place circa 1976.''

January

 * 09 - DWN: Doctor Who - The Gunfighters is first published.

February

 * 02 - Donald Eccles dies.
 * 13 - DWN: Doctor Who - The Time Monster is first published.
 * 16 - Howard Da Silva dies.

March

 * 13 - DWN: Doctor Who - The Twin Dilemma is first published.

April

 * 10 - DWN: Doctor Who - Galaxy Four is first published.

May

 * 14 - William Lindsay dies.
 * 15 - DWN: Doctor Who - Timelash is first published.
 * TC: Turlough and the Earthlink Dilemma is first published. Turlough and the Earthlink Dilemma is the first release of a planned spin-off series of original novels called "The Companions of Doctor Who". As such, this book is the first original novel based upon characters from the TV series (discounting shorter works released in annuals).
 * REF: Doctor Who: The Early Years is first published.
 * 24 - Robert Holmes, widely considered one of Doctor Who's best scriptwriters, dies. His last work was episode 13 of DW: The Trial of a Time Lord, aka episode 1 of DW: The Ultimate Foe.
 * Around the time of Holmes' death, Eric Saward resigns as script editor due to a disagreement with John Nathan-Turner over Saward and Holmes' plans for the final episode of the Trial story arc; Nathan-Turner commissions Pip and Jane Baker to write the final chapter.
 * 31 - Sylvia Coleridge dies.

June

 * Severn House launches Make Your Own Adventure with Doctor Who, a series of "interactive" books in which readers made decisions every few pages that directed the storyline. The first two books published are Search for the Doctor and Crisis in Space. Later in the year, US publisher Ballantine reissues the books (in different order) under its Find Your Fate line.
 * 11 - Reed De Rouen, who played Pa Clanton in DW: The Gunfighters, dies.
 * 12 - DWN: Doctor Who - The Mark of the Rani is first published.
 * 23 - Nigel Stock dies.

July

 * 10 - DWN: Doctor Who - The King's Demons is first published.
 * 17 - REF: Travel Without the TARDIS is first published.

August

 * Garden of Evil and Race Against Time, books three and four of the Make Your Own Adventure with Doctor Who line, are first published.
 * 14 - Production concludes on the 14-part DW: The Trial of a Time Lord. Unknown to most at the time, this will also conclude Colin Baker's involvement with the series.
 * 21 - DWN: Doctor Who - Slipback is first published. Adapted from the radio play of the same name, this is the first novelisation of a Doctor Who story not produced for television. (Note: REF: Howe's Transcendental Toybox says 14th August release.)
 * 22 - REF: Doctor Who - Special Effects is first published.
 * Marvel Comics in the United States publishes the 23rd and final issue of Doctor Who, a monthly series of reprints of comic strips and other material from Doctor Who Magazine. Discounting distribution of imported works from the UK published by Marvel UK and, later, Panini, the next Doctor Who comics published specifically for the American market would not appear until IDW Publishing began its own series of DWM reprints and original works in 2007.

September

 * 06 - DW: The Mysterious Planet Episode 1 (aka The Trial of a Time Lord Episode 1) is first broadcast, launching the belated Season 23. The series returns to its original 25-minute episode format and the number of episodes per season is increased from 13 to 14. However, given the actual episode length reverted back to 25 minutes, this has resulted in a considerably shortened season in comparison to the 1984 and previous seasons. The Trial of a Time Lord, although not the first season to consist of a single story arc (see The Key to Time), is the first time only one on-screen title would be used for an entire season, although the fanbase and producers would divide the tale into four stories. A new arrangement of the theme music, by Dominic Glynn, is introduced. Lynda Bellingham, as The Inquisitor and Michael Jayston, as The Valeyard, are introduced and become regulars for this season. Sabalom Glitz is introduced. First fall debut for a new season of Doctor Who since 1980.
 * 11 - DWN: Doctor Who - The Savages is first published.
 * TC: Harry Sullivan's War is first published. Harry Sullivan's War is the second of three releases under the Companions of Doctor Who spin-off line, and is written by Ian Marter, who also portrayed Harry Sullivan in the TV series more than a decade earlier. Marter died a few weeks later, making this the final book released (but not the final book written) in his lifetime.
 * 13 - DW: The Mysterious Planet Episode 2 (aka The Trial of a Time Lord Episode 2) is first broadcast.
 * 18 - REF: The Doctor Who File is first published.
 * 20 - DW: The Mysterious Planet Episode 3 (aka The Trial of a Time Lord Episode 3) is first broadcast.
 * Dennis Spooner dies.
 * 27 - DW: The Mysterious Planet Episode 4 (aka The Trial of a Time Lord Episode 4) is first broadcast.
 * 28 - Denis Carey dies.
 * 29 - Doctor Who Collected Comics, a reprinting of several Doctor Who Magazine strips, published by Marvel Comics.

October

 * Mission to Venus and Invasion of the Ormazoids, books five and six of the Make Your Own Adventure with Doctor Who line, are first published. Severn House discontinues the line after these books.
 * According to The Television Companion by Howe and Walker, at some point this month, Colin Baker is informed that his contract to play the Doctor is not being renewed.
 * 04 - DW: Mindwarp Episode 1 (aka The Trial of a Time Lord Episode 5) is first broadcast.
 * 06 - Around this time, BBC Controller Michael Grade approaches the originator of Doctor Who, Sydney Newman, for ideas on how to revitalize Doctor Who. In a letter dated 6th October, Newman provides some ideas and suggests he be brought on board as executive producer of the series. He also attempts to be credited as the show's creator. Subsequent meetings, however, fail to result in Newman's return to direct involvement in the series.
 * 08 - Michael Obiora is born.
 * 11 - DW: Mindwarp Episode 2 (aka The Trial of a Time Lord Episode 6) is first broadcast.
 * 16 - DWN: Doctor Who - Fury from the Deep is first published. Promoted as a "bumper volume" due to a higher word count than most Target Books releases up to this time.
 * 18 - DW: Mindwarp Episode 3 (aka The Trial of a Time Lord Episode 7) is first broadcast.
 * 25 - DW: Mindwarp Episode 4 (aka The Trial of a Time Lord Episode 8) is first broadcast. Nicola Bryant leaves the series with this episode.
 * 28 - Ian Marter, who played companion Harry Sullivan and also wrote numerous novelisations for Target Books, dies from a diabetes-related heart attack in London. He leaves behind several Target manuscripts which are published posthumously over the next couple of years.

November

 * REF: Doctor Who: The Companions is first published.
 * 01 - DW: Terror of the Vervoids Episode 1 (aka The Trial of a Time Lord Episode 9) is first broadcast. Debut of Bonnie Langford as Melanie Bush. Mel becomes the first companion whose first meeting with the Doctor is never chronicled on television. Honor Blackman, who starred in the Sydney Newman-created The Avengers, guest stars.
 * 08 - DW: Terror of the Vervoids Episode 2 (aka The Trial of a Time Lord Episode 10) is first broadcast.
 * 11 - Paperback publication of REF: The Doctor Who Cookbook.
 * 15 - DW: Terror of the Vervoids Episode 3 (aka The Trial of a Time Lord Episode 11) is first broadcast.
 * 20 - DWN: Doctor Who - The Celestial Toymaker is first published.
 * 22 - DW: Terror of the Vervoids Episode 4 (aka The Trial of a Time Lord Episode 12) is first broadcast.
 * 29 - DW: The Ultimate Foe Episode 1 (aka The Trial of a Time Lord Episode 13) is first broadcast. This is the final episode to carry a writer credit for the late Robert Holmes, and is also the last episode to credit Eric Saward as script editor.

December

 * US edition of REF: Doctor Who: The Companions is first published.
 * 04 - DWN: Doctor Who - The Seeds of Death is first published.
 * 06 - DW: The Ultimate Foe Episode 2 (aka The Trial of a Time Lord Episode 14) is first broadcast, concluding Season 23. Although not widely known at the time, this would be Colin Baker's final appearance in the series. This also marked the final use of Dominic Glynn's short-lived theme arrangement and the neon-tubing series logo that had been in place (with adjustments upon Baker's arrival) since 1980. Lynda Bellingham and Michael Jayston, having spent the full season as regular cast members, take their leave.
 * The BBC announces that Colin Baker will not be returning as the Doctor in the next series.
 * 14 - Dermot Tuohy dies.
 * 26 - Leslie Dwyer dies.