Somma, born and raised in South Africa before moving to Florida as a schoolboy, had returned home to the US after scoring nine goals in 13 matches for Lincoln while on loan last season.
He then struggled to get back to the UK in time for pre-season training before the intervention of the Labour MP for Leeds Central.
Somma said: "My green card had expired and I had to get that sorted otherwise I couldn't have gone back to the United States. I'd like to thank Hilary Benn, who has helped out a lot. What he did over here really helped things happen quickly and I'd like to thank him for that because it has all worked out.
"I've been training a little bit, but I can't wait to start training with the lads now. I enjoyed my time at Lincoln last season, but I can't wait to make the step up here now."
Source: PA
Source: PA