Gainsborough is a constituency^{[n 1]} in Lincolnshire represented in the House of Commons of the UK Parliament since 1983 by Sir Edward Leigh, a Conservative.^{[n 2]}

The constituency was created under the Redistribution of Seats Act 1885 that year, which lasted until it was reformed as Gainsborough and Horncastle on a boundary change for the 1983 election. That seat lasted until 1997, as from the mid-1990s population changes led to removal of Horncastle from the seat and recreation of the old seat with largely similar boundaries.

1885–1918: The Municipal Borough of Lincoln, the Sessional Divisions of Epworth, Gainsborough, Lincoln, and the parish of Bracebridge.

1918–1950: The Urban Districts of Crowle and Gainsborough, and the Rural Districts of Gainsborough, Isle of Axholme, and Welton.

1950–1983: The Urban Districts of Gainsborough and Market Rasen, and the Rural Districts of Caistor, Gainsborough, Isle of Axholme, and Welton.

1997–2010: The District of West Lindsey, and the District of East Lindsey wards of Binbrook and Wragby.

2010–present: The District of West Lindsey, and the District of East Lindsey ward of Wragby.

This constituency is named for its largest town of Gainsborough, on the west edge of the constituency, and comprises the West Lindsey district, and the Wragby ward of the East Lindsey district.

This relatively vast rural seat north of Lincoln is named after the small market town at its western boundary. Regeneration projects are attempting to reduce pockets of severe deprivation in the constituency, but most of the area is affluent, albeit remote from many major cities; the closest conurbation is the city of Lincoln to the immediate south. Scunthorpe and Grimsby are both close enough to the northern edge of the constituency to be significant to residents. Though arable farming dominates the landscape and noteworthy pig farming industry (see Lincolnshire sausages), agriculture is in decline and the service/creative sector dominates.^[4] The seat has elected Conservative MPs since 1924 and is a stronghold, as well as giving its MPs very long tenures, having been represented by only three people since 1924.

• List of parliamentary constituencies in Lincolnshire
• The town of Gainsborough, Lincolnshire