Head of the Zionist delegation at the Paris Peace Conference in Versailles, which tried to obtain international approval for the Balfour Declaration.

Heads the Zionist Commission for Palestine, a delegation that traveled to the Palestine at the initiative of the British Government with the aim of making recommendations regarding the settlement and development of the country. In a letter to his wife, Vera, he described what he was seeing: “The difference between what you can see today in the settlements, and what it was possible to see when I was first here eleven years ago, is astounding. Today, these settlements are filled with life. Real Jews are living here. They are no longer a legend; they are real!” 

Becomes President of the British Zionist Federation, an organization that was established after Britain conquers the Palestine from Ottoman rule. Conducts negotiations with the British Government which end on November 2nd with the granting of the Balfour Declaration. 

The birth of his second son, Michael. Manages the British Admiralty’s laboratories in London. Begins a campaign, with the help of friends, to spread the idea of creating a Jewish national homeland in the Palestine under British patronage. 
Meets with Prime Minister Lloyd George and Foreign Secretary Balfour.

Invents a new method for producing acetone, a solution that was essential for the production of explosive materials. 
Moves to London and is appointed as an advisor to the British Admiralty and Ministry of Munitions for the supply of acetone.

Works, with the outbreak of World War I, to promote the idea of a Jewish national homeland in the Palestine that is under British patronage.

Receives British citizenship.

The birth of his eldest son, Benjamin (Benjy). Becomes famous as a representative of Synthetic Zionism at the Eighth Zionist Congress at The Hague. 
Visits the Palestine for the first time. “I traveled by boat from Beirut to Jaffa. My feet stepped on the land that had been, since the days of my childhood, an inseparable part of my thoughts. Finally, I was face-to-face with reality. I came to the firm decision that I should return to Europe and continue to increase the pressure—with double the energies–for urgent, practical work in the Palestine.”

Marries Vera Chatzman, whom he had met in Switzerland, where she was studying medicine. “Vera and I found our way to each other but slowly, partly because of the seven-year difference in our ages and in our positions, as I was a lecturer and she was a student, but primarily because of differences in our background and approach to life.” 
That same year, Dr. Weizmann meets Arthur James Balfour, The former prime minister of UK, and explains to him the Zionist idea. “He asked me, ‘Why are the Jews opposed to the Uganda Plan?’”  

Moves to England and works as a researcher in the Chemistry Department at the University of Manchester.