"The versatile 21-year-olds have both put pen-to-paper on four-year deals and become David Moyes' second and third signings as Sunderland manager," the club said in a statement.
Northern Ireland international McNair, who can also operate in midfield, heads to the Stadium of Light with two seasons of Premier League experience at Old Trafford.
"Paddy is a young, athletic player who is improving all the time. He has experience for Northern Ireland and we want to bring as many international players to the club as we can," Moyes said.
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Scotland under-21 international Love, who can play at full-back or in midfield, made his senior debut for Manchester United last season, playing in both the Premier League and Europa League while also enjoying a successful spell on loan at Wigan Athletic.
"I want to add some young players to the squad as well as some senior players and both of them have got really good potential and the opportunity to improve," said Moyes, who signed Senegal defender Papy Djilobodji from Chelsea on Friday.
Sunderland begin their Premier League campaign with a trip to Manchester City on Saturday.
(Reporting by Amlan Chakraborty in New Delhi; editing by Sudipto Ganguly)
