The U.S. Constitution grants the president of the United States the power to appoint ambassadors, as spelled out in Article II, Section 2. Congress does not have that power; however, the first stage of the process of appointing an ambassador is nomination. The president must nominate someone to be ambassador, but that nomination does not proceed to full appointment until after the U.S. Senate confirms it. The House of Representatives does not play a role in nominating or confirming ambassadors.
Naming an Ambassador
This system is part of the Constitution’s checks and balances, which ensure that no single branch of the federal government gains excessive power over the other two. The specific wording of the Constitution is that the president appoints an ambassador “with the advice and consent of the Senate,” and that terminology is important, because it implies senators’ full participation in the process. A president may seem to circumvent that “advice and consent” by making appointments to diplomatic vacancies that occur while the Senate is in recess, but such recess appointments are only temporary, expiring at the end of the next Senate session.