Master chief petty officer (MCPO) is the ninth (just below the rank of MCPON) enlisted rank (with pay grade E-9) in the United States Navy and United States Coast Guard, just above Senior Chief Petty Officer (SCPO).

[1] Prior to 1958, chief petty officer was the highest enlisted rate in both the U.S. Navy and U.S. Coast Guard.

It carries requirements of time in service, superior evaluation scores (based on rater giving the evaluation, fluid variables for criterion and other factors including but not limited to community involvement), and selection by a board of master chiefs.

In the Coast Guard, advancement to master chief petty officer is done by competing in a single annual board.

It is not uncommon practice to refer to the master chief by this shorthand in all but the most formal correspondence (such as printing and inscription on awards).

On other uniforms, the insignia used for shirt collars and caps is the one that has become universally accepted as the symbol of the chief petty officer.

In this capacity, the CMC assists the commanding officer in issues of quality of life, discipline, training, and morale.

The holder of this post is appointed by the Chief of Naval Operations (CNO) to serve as the most senior enlisted member in the Navy.

As of 2023[update], the current master chief petty officer of the Coast Guard is Heath B. Jones.