The midfielder, who has signed a pre-contract agreement at Tannadice, has played a key part in winning promotion with Partick this season, scoring 14 goals for the Jags.
And now the 26-year-old is relishing a new challenge with United and is looking forward to linking up again with the former Thistle management team of Jackie McNamara and Simon Donnelly.
"I'm looking forward to the challenge," Erskine told the Dundee Courier.
"Obviously it was a hard decision to leave, I've had four years at Thistle and I've loved every second of it.
"I felt it was right for me to move on and try and further my career and I think that's what I'm going to do.
"Jackie and Simon are up there and I really enjoyed working with them at Partick. They probably got the best out of me so teaming up with them again is going to be good."