By definition it's a "rotter" or a despicable person. In reality in English it's a colloquialism that affords itself to a more a luckier fellow. Much like a 'bugger' whilst the roots of the word are offensive, the actual use is endearing. A lucky 'git', a wealthy 'git' and a sodding 'git'... when used right is still a mate. A friend.
It's more positive these days.
The origins are from the word 'geat' which were a Scandinavian people living in Götaland, land of the Geats, currently within the borders of modern Sweden. The name of the Geats lives on in the Swedish counties of Västergötland and Östergötland, the Western and Eastern lands of the Geats, as well as in many toponyms.
Shut yer face you lucky git.