After World War 2 there was rapid population expansion, with Wainuiomata earning the nickname 'Nappy Valley' because of the large number of families with young children.

The origins of the word are disputed, but one commonly accepted translation refers to the women who came over the Wainuiomata Hill to evade marauding tribes from the north, and who sat wailing by the stream after the slaughter of their menfolk.

One source says there is evidence Māori were in Wainuiomata from the moa-hunting period and the iwi Rangitane, Ngāti Ira and Kahungunu were all settled there.

[6][7] The earliest European settlements grew up around the river, where timber mills supplied the Wellington region when the demand was great in the 1850s and '60s.

[8] The town's economy in these early days largely depended on timber milling from the forests around the Wainuiomata River.

In the 1850s Sir William Fitzherbert started a flax-milling business in the north of the valley,[9] but this proved economically unviable.

In 1866 the Methodist Wainuiomata Coast Road Church was built on land donated by settler Richard Prouse.

After World War II ended in 1945, major growth occurred due to affordable housing developments attracting many young couples, which transformed Wainuiomata into a working-class community.

[16] In April 2009 a Palmerston North hotelier banned all Wainuiomata residents after a series of misdemeanours by visitors from there.

[17] The first series of the television production Seven Periods with Mr Gormsby was shot in the old Wainuiomata College with many local residents as cast members.

[18] In 2022, a study commissioned by Wellington Regional Council and conducted by Jim Lynch, the founder of Zealandia, found that establishing a wildlife sanctuary in the Wainuiomata Water Collection Area was "technically and practically feasible".

The Wainuiomata ward covers the suburb and the surrounding rural area, electing one councillor to the Hutt City Council.

Several factories that operated in Wainuiomata during the second half of the twentieth century closed down in the late 1980s and 1990s after changes in government regulation of imported goods.

[33] Wainuiomata entered a long period of economic stagnation and population decline, but since around 2020 the suburb has seen new development, including a revamped town centre, a new retirement village and a building boom as new areas are opened up for housing and older bungalows are demolished to make way for medium density townhouses.

[44] The company faced challenges in the 1980s after the government changed its regulation of imported footwear, and the Wainuiomata factory closed in 1992.

[45][44][46] Tatra, founded by Frederick Turnovsky, produced leather accessories such as belts and wallets at a factory in Wainuiomata which operated between the 1960s and 1980s.

[48] Tatra went into receivership in 1988, after a downturn in business due to competition from cheap imported leather goods.

[54] Tom & Luke is a snack food manufacturer based in Wainuiomata that sells its products in New Zealand and exports to Australia, Asia and the United States.

[63] The main pool was extended to Olympic length in the early 1970s, and after more community fundraising, an 80 metre hydroslide was added in 1984.

The park contains swimming spots, walking and cycling trails, as well as access to a disused dam which used to be part of the system supplying Wainuiomata and Wellington City with water.

Wainuiomata has a popular mountain biking venue at Waiu Park in the hills in the north-west of the suburb.

The Wainuiomata Trail Park was developed as a joint initiative by a volunteer group and the Hutt City Council.

Rugby league was particularly prominent in the 1980s and 1990s, with the Wainuiomata Lions team winning a national title three times, but its popularity has waned since then.

[70] In 2019 a four-metre wide shared walking and cycling path over the Wainuiomata Hill Road was completed.

The path, called Te Hikoi Arawera ('Pathway to the horizon') cost $12.9 million and was funded by Hutt City Council and the New Zealand Transport Agency.

At the top of the hill is the Pukeatua pedestrian bridge, completed in 2015, and then the path continues down the harbour side of the road to Gracefield.

[74][75][76] Queen Street is Wainuiomata's main shopping area, and there is also a public library and community centre with a large hall.

It had no flashing lights, only a siren, and on occasions this failed: it was not unusual for members to yell from the truck "get out of the way", or words to that effect.

[84][87] Iritana Te Rangi Tāwhiwhirangi DNZM MBE and Wainuiomata resident Jean Puketapu started Pukeatua Kōhanga Reo together.

[90] By the 40th anniversary in 2022 Pukeatua Kōhanga Reo had moved to a bigger premises and was led by Kuini Garthwaite (Ngāti Porou).