As well as being the 6pm co-host, Hayes will continue to report on leading issues.
A MediaWorks spokesperson said a decision on a permanent replacement for Hayes on Newshub Late would be made "in the near future".
McRoberts said he was looking forward to working with Hayes.
"For me the challenge of life after Hilary is a positive one.
"I'm lucky that I'm surrounded by wonderful colleagues and I'm looking forward to helping shape Newshub's future."
Barry signed off from TV3 on Friday, leaving her roles on Newshub and Paul Henry's morning show.
The Herald revealed on April 29 that she was quitting TV3.
Sutherland said Hayes brought a "wealth of experience across news and current affairs".
Given her presenting ability and "own unique style", she would prove to be a "fantastic co-host" with McRoberts.
Barry is widely tipped to take up a new role at TVNZ.
She has previously said that she wants to take time out with her family before confirming her next move.
MC-ing an event in Parnell on Thursday night, Barry told the Herald on Sunday she was battling a wave of emotions before signing off from TV3 for the final tme. "It's like saying goodbye to my family, because I spend more time with my colleagues than my actual family," she joked.