The JLS member picked up a judges' score of 39 out of 40 for a jive to 'Rockin Robin', lifting the trophy with dance partner Ola Jordan.
The pair's routine proved most popular with the BBC One show's studio audience when their votes were combined with the marks given out by the judges.
"It feels really, really, really, really good," said Gill of his victory. "I'm sure the boys will be proud. I loved it, it was an incredible experience."
Strictly's head judge Len Goodman described the routine as "full on and flat-out", adding that the quality was "fantastic" given that the pair had only been training for a week.
Darcey Bussell praised Gill and Jordan's "amazing energy", while Bruno Tonioli was impressed by their "vitality".
Craig Revel Horwood noted that the pair suffered from a "nasty slip" and felt that the routine was "a little bit flat-footed", but praised the "amazing amount of character".
Other celebrities appearing in the Christmas special included former Bolton Wanderers footballer Fabrice Muamba, who danced a salsa with Aliona Vilani.
Blue Peter presenter Helen Skelton and Artem Chigvintsev also performed a jive, while actress Sheila Hancock and Ian Waite joined forces for a foxtrot.
Comedian Bobby Ball danced an American Smooth with Katya Virshilas, and Katy Brand partnered Anton Du Beke on a Viennese Waltz.
Previous Strictly Come Dancing champions Tom Chambers, Chris Hollins and Natasha Kaplinsky were joined by past contestants Rachel Stevens, Kelly Brook, Chelsee Healey, Colin Jackson, Ann Widdecombe and Russell Grant for an all-stars routine.
Rod Stewart also appeared to sing the Christmas standard 'Let it Snow'.