Ings has joined the Hammers for an undisclosed fee, understood to be around £12million, until the summer of 2025.
The 30-year-old is eligible for an immediate debut in Saturday’s crunch home meeting with fellow strugglers Everton.
“I’m really excited to join West Ham United,” said Ings.
“It’s important I settle in as quickly as I can do – and do the important stuff on the pitch for West Ham.
“We’ve got some massive games ahead of us – and I’ve come here to try and score as many goals as I can to help the team to get some positive results.
“I’m really looking forward to getting started.”
Manager David Moyes had previously stated he would not be making too many moves in the January transfer window, but acted after his goal-shy side slipped into the relegation zone.
“I’m really pleased to add Danny to the squad,” he said.
“He is a proven Premier League goalscorer and will add great competition for places in the attacking third.
“We’re looking forward to integrating him into the group, as we go into a busy period in our season.”