Military Justice Improvement Act of 2013

Military Justice Improvement Act of 2013 - Amends the Uniform Code of Military Justice (UCMJ), with respect to charges that allege an offense triable by court-martial (with certain exclusions) for which the maximum punishment includes confinement for more than one year, to direct the Secretary of Defense (DOD) to require the Secretaries of the military departments to provide for the determination of whether to try such charges by general or special court-martial to be made by a commissioned officer of grade O-6 or higher with significant experience in such trials and who is outside the chain of command of the accused. Provides that a determination not to proceed to trial shall not preclude a commanding officer from either referring such charges for trial by summary court-martial or imposing non-judicial punishment.

Requires Rule 306 (relating to policy on initial disposition of offenses) of the Manual for Courts-Martial to be amended to strike the character and military service of the accused from factors to be considered by the disposition authority.

Revises the list of officers authorized to convene general and special courts-martial to include those in grade O-6 or higher assigned such responsibility by their department chief of staff (with the same prohibition against an officer in the same chain of command as the accused). Requires each chief of staff to establish an office which shall convene general and special courts-martial and detail judges and members.

Requires a military judge to call a general or special court-martial trial into session within 90 days of the determination of its necessity.

Requires a convening authority (the official acting on the sentence of a court-martial), when taking any action other than approving a sentence, to prepare a written justification of such action which shall be made part of the record of the court-martial. Prohibits a convening authority from: (1) dismissing or setting aside a finding of guilty, or (2) reducing a finding of guilty to a finding of guilty to a lesser included offense.

Requires a commanding officer who receives a report of a sexual-related offense involving a member in such officer's chain of command to act immediately upon such report by way of referral to the appropriate criminal investigative office or service.

Amends the National Defense Authorization Act for Fiscal Year 2013 to require an independent panel established by the DOD Secretary to monitor and assess the implementation and efficacy of this Act and its amendments.