United have called a media conference at Tannadice for chairman Stephen
Thompson to introduce their new boss.
United were officially granted permission to speak to McNamara by Partick Thistle on Tuesday night, after the former Celtic captain won the race to succeed Peter Houston at Tannadice.
McNamara and Falkirk boss Steven Pressley had been the leading candidates in the past few days and the Jags boss edged in front.
A statement from his club read: "Following an approach from Dundee United, the board of directors of Partick Thistle Football Club have reluctantly granted permission for Jackie McNamara and Simon Donnelly to speak to them about their vacant managerial position."
United face the biggest game of their season so far on Saturday when they host Rangers in the William Hill Scottish Cup fifth round, and were keen to have McNamara in place in plenty of time to prepare for the visit of Ally McCoist's men.
The players and caretaker manager Paul Hegarty endured a fruitless trip towards Motherwell on Tuesday night before their Scottish Premier League clash was postponed because of a waterlogged pitch less than two hours before kick-off.
McNamara has impressed in his first management job after turning Thistle into Irn-Bru First Division title contenders.
The 39-year-old initially took over as caretaker manager from Ian McCall in April 2011 and would leave Thistle in second place in the table, five points behind Morton with two games in hand.
The former Celtic and Scotland player led the Jags to a sixth-placed finish in his first full season in charge.
Houston left on Monday after Thompson grew uncomfortable with the speculation surrounding the club following the announcement that the former Scotland assistant manager would not extend his contract at the end of the season.