Final answer:
General George Washington was selected to be the leader of the Continental Army on June 15, 1775, following John Adams's proposal during the Second Continental Congress.
Step-by-step explanation:
The leader selected to command the Continental Army was General George Washington. On June 15, 1775, during the Second Continental Congress, Washington was nominated and accepted the command of the Continental Army the following day. This unanimous decision was largely influenced by John Adams's proposal to consider the forces in Boston as a Continental army and the recognition of the need for an established general to lead them. Washington's leadership played a pivotal role in the Revolutionary War, with significant battles such as the siege of Boston and the Battle of Harlem Heights proving decisive under his command.