In 1930, Harry Gosling, the sitting Labour MP for the Whitechapel and St Georges constituency in the East End of London died. Janner was chosen to contest the resulting by-election. The area had a large Jewish population, and he campaigned in opposition to the government's policy on Palestine, but was narrowly defeated. Ten months later at the 1931 general election Janner again contested the Whitechapel seat for the Liberals, this time being returned to the House of Commons. At the next general election in 1935 Janner stood as a Liberal and Anti-Fascist candidate, but was one of many Liberals to lose their seats, with the Labour Party regaining the seat.