Boro have paid £5million to West Ham for the 30-year-old where he will receive around £27,000 a week on a four-year contract
Ireland’s keeper made 50 appearances for the Hammers side since joining on a free transfer in 2015 following his release from Birmingham City.
Randolph told his followers on Instagram:
“Firstly I just want to say thank you to all the West Ham fans for their support over the last couple of seasons. I had some great times and experiences at the club but sadly decisions were made that meant I had to cut short my time there to look after myself and my career. I want to wish all the lads all the best for the upcoming season, it has been a pleasure! Looking ahead, it’s a really exciting challenge here at Middlesbrough and I can’t wait to get started!”