The 38-year old, who recently departed Newcastle United after two decades, has signed a one-year deal with the Tigers.
Steve Bruce has already signed Allan McGregor this summer and has now added Harper to compete with the Scotland international for the number one spot.
"We just thought we needed a bit of experience," Bruce told Sky Sports News.
"We let a young kid, Mark Oxley, go to Oldham to get some experience, and we just needed a bit of experience.
"We got in Allan McGregor and now we've brought in Steve, who has been around the Premier League for 20 years.
"He'll be good in the dressing room and good for the younger players we have got in the squad. With his experience, he will certainly help me to try to achieve what we want to achieve."