Final answer:
The 1st Congress passed the Bill of Rights and established the Supreme Court.
Step-by-step explanation:
The major actions taken by the 1st Congress included passing the Bill of Rights and establishing the Supreme Court.
The Bill of Rights refers to the first ten amendments to the United States Constitution, which guarantee individual rights such as freedom of speech, religion, and the right to a fair trial.
The establishment of the Supreme Court under the Judiciary Act of 1789 created a judicial branch that would interpret and uphold the Constitution.