The 22-year-old Gambian signed on a short-term deal, set to expire this month, from Swedish side Ostersunds FK last summer.
The striker has featured in three Premier League games for the Swans this season and has impressed manager Garry Monk.
And the player has spoken of his delight at the deal with his family having settled successfully in South Wales.
???I???m delighted. It’s great to sign a new contract and it was an easy decision,??? Barrow said.
???My girlfriend and I really like it here and we are really happy. I came here until January initially but now I can settle for the next four years.??
???It???s been amazing to play for the first-team and I have tried to work as hard as possible in training and when I???ve been given my chance.
???But I know I must keep working for further opportunities.???