The 28-year-old has agreed personal terms on a deal three-year-deal after turning down the chance to join a number of other Premiership clubs.
Neill started his full-time carear at Millwall making over 150 appearances for the Lions before moving to Blackburn in 2001.
Lucas is looking forward to the challenge of keeping the Hammers in the Premiership.
“I get the feeling that I am going to fit in well at West Ham United and be an important member of the squad,” he told the official site.
“At this stage of my career, playing regularly is very important to me and I don't feel that I will be a bit-part player here.
“I just have a gut feeling and a sense of warmth about this move. It's an exciting time for everyone at West Ham United to look forward to. Short term, we are in a tough position but there is already a great squad here and, with the players who have signed during January, I'm sure we will lift ourselves out of it soon.
“Come the summer, I think people are going to be talking about West Ham United with a completely different terminology.”