Harrow was a constituency of the House of Commons of the UK Parliament 1885—1945 in Middlesex, a traditional county; it covered an area forming part of the north-west of today's Greater London.

[1] Ambrose is appointed Attorney-General of the Duchy of Lancaster, requiring a by-election.

Ambrose resigned after being appointed as a Master in Lunacy, requiring a by-election.

The political parties had been making preparations for an election to take place and by July 1914, the following candidates had been selected; Chamberlayne was nominated by the non-party Harrow Electors League General Election 1939–40 Another General Election was required to take place before the end of 1940.

The political parties had been making preparations for an election to take place and by the Autumn of 1939, the following candidates had been selected;