The Northern Ireland man has spent time with West Ham from 2006-08 as well as
a brief stint with the Hammers last season on a short-term contract during
which he helped the club gain promotion to the top flight.
'I am delighted to be coming back to West Ham and this time on a permanent
basis,' McCartney said. 'It was great to be part of the side that won
promotion for the club last season.
'It was a fantastic way to end the campaign last year and I am really looking
forward to being back in the Premier League with West Ham.'
The 31-year-old becomes the fourth signing of the summer for manager Sam
Allardyce, joining Jussi Jaaskelainen, Stephen Henderson and Mohamed Diame.