A service member who pleads guilty at a general or special court-martial may later want to take that plea back. The rules treat a request to withdraw very differently depending on when it is made. The narrowest and most difficult window is the one this question asks about: after the military judge has announced the sentence but before the post-trial process is complete. Understanding how that window works requires separating two ideas that often get blurred together, the timing of the withdrawal request and the modern role of the convening authority.
The governing rule and its timing test
Withdrawal of a plea is governed by Rule for Courts-Martial (RCM) 910, the same rule that controls how pleas are entered and accepted. RCM 910 draws a clear line at the moment sentence is announced. Before the sentence is announced, a military judge may permit an accused to withdraw a guilty plea for any fair and just reason, a relatively forgiving standard. Once the sentence has been announced, the standard tightens considerably. After announcement of sentence, the accused may withdraw the plea only upon a showing that withdrawal is necessary to correct a manifest injustice.
That phrase, manifest injustice, is the heart of the matter for the period described in the question. The request is being made after the sentence is adjudged, so the lenient pre-sentence standard no longer applies. The accused carries the burden of persuading the military judge that allowing the plea to stand would work a manifest injustice, for example because the plea was not knowing or voluntary, because the factual basis for the plea collapsed, or because a material term of the plea agreement cannot be fulfilled.
Why the convening authority no longer “approves” the sentence
The way this question is phrased reflects the old military justice system, and the answer has changed in an important way. Under the rules that applied before the 2019 Military Justice Act, the convening authority took formal action to approve, disapprove, or reduce the sentence, and that action was a meaningful checkpoint. The Military Justice Act of 2016, which took effect on January 1, 2019, fundamentally altered that structure.
Under the current framework built on Article 53a and Article 60a of the Uniform Code of Military Justice, the convening authority no longer approves the sentence in the traditional sense. Once a military judge accepts a plea agreement, the agreement binds the parties …