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Baron Lionel Nathan de Rothschild was a British banker and politician. He became the first practising Jew to sit as a Member of Parliament in the United Kingdom.
In 1847 Lionel de Rothschild was first elected to the British House of Commons as one of four MPs for the City of London constituency. Because Jews were at that point still barred from sitting in the chamber due to the Christian oath required to be sworn in, Prime Minister Lord John Russell introduced a Jewish Disabilities Bill to remove the problem with the oath. In 1848, the bill was approved by the House of Commons but was twice rejected by the House of Lords. After being rejected again by the Upper House in 1849, Rothschild resigned his seat and stood again winning in a by-election to strengthen his claim.
In 1850, he entered the House of Commons to take his seat but refused to swear on a Christian Bible asking to use only the Old Testament. This was permitted but when omitting the words "upon the true faith of a Christian" from the oath he was required to leave.
Rothschild was reelected in 1852, but did not take the oath until 1858, after the House of Lords agreed to a proposal to allow each house to decide its own oath. On July 26, 1858, Rothschild took the oath with covered head, substituting “so help me, Jehovah” for the ordinary form of oath, and thereupon took his seat as the first Jewish member of Parliament. He was re-elected in general elections in 1859 and 1865, but defeated in 1868; he was returned unopposed in a by-election in 1869 but defeated a second time in the general election in 1874.
https://www.jewishvirtuallibrary.org/lionel-nathan-de-rothschild