The northern boundary follows Clapham Park Road, Acre Lane, and Coldharbour Lane through Clapham and Brixton to Lambeth Town Hall. The north-eastern boundary generally follows Effra Road and Tulse Hill, but runs east of the main road to include the part of the Tulse Hill estate and the Cressingham Gardens estate west of Brockwell Park. The boundary skirts the Tulse Hill district centre, following Hardel Rise, Christchurch Road and Norwood Road, and then runs along Leigham Vale and Leigham Court Road. The southern and western constituency boundaries follow Lambeth's borough boundaries with Croydon, Merton and Wandsworth.
9 Liberal Democrat councillors represented the wards of Streatham Hill, Streatham Wells and St Leonard's with one additional councillor elected at Clapham Common in 2010. All Streatham wards had been represented by the Liberal Democrats from 1990 to 2014 before Labour subsequently gained seven seats from them at the 2014 council elections. The Liberal Democrats were unsuccessful in gaining any seats back at the 2018 local elections. In a 2019 Thornton Ward by-election, the Lib Dems came within 19 votes of winning the seat.
In 2018, the Conservatives held one seat and lost two to Labour in Clapham Common, by a very narrow margin, whilst the Greens took the other two seats from Labour in St Leonard's.
Streatham was for a few decades solidly Tory suburbia overall - the Conservatives won Streatham when Labour gained large majorities in 1945 and 1966, and it was the only seat in the former LCC area (Inner London) apart from the Chelsea/Kensington/Westminster/City central core to remain consistently Conservative.
The Conservative Party lost Streatham in 1992, having held it since 1918. The Conservative candidate was beaten into third place by a Liberal Democrat in 2001, and there were swings from Labour to the Liberal Democrats at the two subsequent general elections. An improvement in the Conservative share of the vote took place in 2010, when the Labour incumbent, Keith Hill, retired and Chuka Umunna was elected standing with the party. The 2015 result was the re-election of Umunna, which made the seat the 96th safest of Labour's 232 seats by percentage of majority.
Demographic and voting pattern changes combined with unfavourable boundary changes converted Streatham into a marginal seat, then into a mid-ranking safe Labour seat. However, in 2015 the Conservatives moved into second place with a sharp increase in numerical vote share, and remained there in 2017.
The constituency of Streatham was contested under the name at the 1918 general election when it approximately followed the historic parish boundaries of Streatham, including a substantial part of Balham, a 19th-century founded primarily urban parish by 1918.
The rest of the constituency, including the town of Streatham has since 1965 been in the London Borough of Lambeth. Three other constituencies covered Lambeth from 1974, Vauxhall, Norwood and Lambeth Central. The Clapham constituency was abolished as part of the 1974 changes. The Clapham Park area and Hyde Farm (commonly thought of as part of Balham) came into the Streatham seat, whereas the rest of Clapham went into the Vauxhall seat creating an enduring split.
On abolition of Lambeth Central at the 1983 election, the constituency gained much of southern Brixton. Following further population decline, Lambeth was paired with Southwark in the next boundary review, and from the 1997 election, Streatham constituency gained areas around Tulse Hill from the former Norwood constituency, the rest of which became part of Dulwich and West Norwood.
Among the most ethnically diverse constituencies, Streatham - which covers parts of Clapham, Balham, Brixton, Tulse Hill and Streatham itself - is in the south London borough of Lambeth. Only 58.2% of residents are white and it has among the most mixed race and black residents in the country, according to the 2011 Census. It has Polish, Portuguese and Hispanic communities.
The bulk of residents are aged 25–44, with relatively few pensioners. Although it is a residential area, it is more popular with young workers than families, having good transport links into central London. Many residents rent and there is a large social housing sector. Streatham High Road is home to over 400 businesses. A £26m ice rink and leisure centre opened in November 2013, part of continuing investment. The population is highly qualified and a high percentage are in full-time work.