He will battle with current Conservative MP Caroline Nokes and Liberal Democrat candidate Ben Nicholls.
Caroline Nokes is the Conservative incumbant
Councillor Paffey was first elected to the city council in the Peartree ward in 2011, and has been a member of the Labour party since 2007.
Born in the north east, he moved to Hampshire as a youngster and then moved to Southampton while a student.
The 36-year-old is currently a lecturer in Spanish and linguistics at the University of Southampton.
Speaking after he was selected to stand by constituency party members, he said: “It is an honour to be selected by Labour members to contest Romsey and Southampton North at the General Election.
“We have a Government with poor priorities. They stand up for the wrong people, defending bankers’ bonuses and handing out tax cuts to the very richest, while so many working families are worse off and the most vulnerable have their welfare payments slashed.
“Families are forced to pay a bedroom tax, yet big businesses are let off from paying their fair share. Voting Lib Dem or voting Conservative: it’s all the same now, and neither party seems to understand how tough things are for working people.
“I will fight to protect our NHS, and campaign on local issues like housing and fracking wells. I look forward to meeting local residents over the next year to offer Labour’s alternative and to send a message to this Government that Britain needs change.”
“A vote for Labour will send a message that ordinary families are worse off since David Cameron became Prime Minister and things aren’t getting any easier.”