What did Doctor Who's companions do next?

Played Captain Jack Harkness (2005, 2007-2008, 2010)

Introduced in the first series as a conman, the wildly flirtatious Captain Jack Harkness quickly became such a firm favourite amongst fans that actor John Barrowman was awarded his own spin-off series Torchwood, which ran until 2011.

Barrowman's popularity in the role saw the 51-year-old become a TV personality in his own right, starring in 2010’s Christmas edition of Strictly Come Dancing, guest-presenting The One Show in 2016 and appearing as a panelist on Celebrity Juice.

https://www.youtube.com/watch?v=D5J9h0HPklE

As well as this, John also went on to star as Patrick Logan in Desperate Housewives, and Malcolm Merlyn in TV series Arrow. He's also a well-loved regular on the Comic-Con circuit.

Catherine Tate

Played Donna Noble (2006, 2008-2010)

Initially appearing in the 2006 Doctor Who Christmas special as The Runaway Bride, Catherine Tate reprised the role of Donna Noble to play the Tenth Doctor's companion in 2008.

Sharing a strictly platonic relationship with David Tennant’s Doctor, Tate, 50, bowed out of the show in 2010 to focus on other projects.

Returning to comedy by starring in the US edition of The Office as Nellie Betram between 2011-2013, Tate also reprised comedy character ‘Nan’ from The Catherine Tate Show for a series of specials.

https://www.youtube.com/watch?v=tHdPbClbFtk

She also starred alongside David Walliams in BBC drama Big School, where she played Miss Sarah Postern.