Final answer:
John Adams served as a Harvard lawyer defending the British soldiers after the Boston Massacre, contributed as a delegate to the Continental Congresses and was involved in creating the Declaration of Independence, and worked as a diplomat in Europe securing support for America.
Step-by-step explanation:
Before becoming President, John Adams served the United States in several significant capacities. Firstly, he established his reputation as a Harvard lawyer, gaining prominence by defending the British soldiers involved in the Boston Massacre. This act demonstrated his commitment to the principle of fairness in the application of law, regardless of public sentiment.
Secondly, Adams was a delegate to the Continental Congresses, where he played a crucial role in pushing for American independence when others were hesitant. His contribution to these Congresses also involved him being part of the committee tasked with writing the Declaration of Independence, a foundational document of the United States. Lastly, his diplomatic skills were put to use when he served as a diplomat in Europe, helping to secure vital international support for the new nation through his work in Holland, France, and Britain.