David and Georgia met on the set of the Doctor Who episode 'The Doctor's Daughter' in November 2007. She played his character's daughter. Around that same time David started dating BBC Wales staffer Bethan Britton, but that relationship ended six months later. David and Georgia then started spending time together as friends, but did not start dating till months later (due to Tennant's shyness, according to Georgia's father Peter Davison, though he dated other women during those months).
They dated casually off and on for around two years, mainly long-distance, before Georgia fell pregnant unexpectedly in June 2010 shortly after David moved to the US alone to pursue an American career. He subsequently moved back to the UK and decided to start a serious relationship with Georgia in order to create a family for his child. They got engaged on Christmas Day 2010, and moved in together the following January. Georgia gave birth to their daughter Olive two months later. They got married in a small private registry office ceremony on December 30th 2011, followed by a reception/new year party at the Swan restaurant next door to the Globe Theatre in London, a day later.
Tennant also adopted Moffett's older son, Ty (a child actor), and Moffett had his surname changed to Tennant's stage name by deed poll. Seven months after the wedding she fell pregnant again, giving birth to her third child Wilfred on 2 May 2013.
They had a temporary separation in January 2014, both dating other people, but got back together that summer.
David is notoriously private about his love life and has never spoken about Georgia, and avoids being photographed with her via refusing to pose together, never walking red carpets together, entering and leaving events and public buildings separately, and walking down the street some distance apart, in an attempt to keep their privacy and keep their relationship out of the media. However Georgia and her friends and family regularly talk about the couple and their family in interviews and online, and Georgia regularly talks about David and the children and posts photos of them to her public Facebook page.