The by-election triggered by former foreign secretary David Miliband’s departure from the Commons is to be held on May 2.
Labour sources said Mr Miliband would formally vacate the South Shields seat on Monday, and the writ would then be moved for the contest. Emma Lewell-Buck was selected as the party’s candidate for the safe seat earlier this week.
Mr Miliband made the surprise announcement that he was leaving Britain to run the New York-based International Rescue Committee last month. He has not served on the Labour front bench since narrowly losing to brother Ed in the 2010 leadership contest – although some supporters still harboured hopes that he would return.
Mr Miliband will apply to the Treasury for the position of Steward of the Manor of Northstead, the traditional mechanism for resigning from the Commons.
He had an 11,109 majority at the last general election.