Unilever claims the acquisition will make it the world leader in hair conditioning, the second-largest global company in shampoo, and the third-largest in styling.
In the UK, the company claims the addition of brands such as VO5, Tresemmé and Simple will enable it to cover more price points across more categories.
Paul Polman, chief executive of Unilever, said: "We are delighted to be acquiring Alberto Culver. Their people have done an excellent job of building an impressive range of brands such as Tresemmé, VO5, Nexxus, St Ives and Simple.
"These will complement Unilever's existing portfolio of iconic brands like Dove, Clear and Sunsilk in hair care and Pond's and Vaseline in skin care, and will help build on our strong global positions in hair care and skin care categories."
Last year Unilever agreed to acquire the personal care division of Sara Lee for €1.28bn, but has not yet completed the deal due to regulatory hurdles in Europe. The Sara Lee division owns brands including Brylcreem, Sanex and Carex.
Alberto Culver's headquarters are in Illinois in the US. Its UK office is based in Basingstoke. It was founded in 1955 around the haircare brand Alberto VO5 and has grown into a global company that generated sales of $1.6bn and earnings before interest, taxes, depreciation and amortisation of more than $250m in the 12 months to 30 June 2010.
It acquired Simple, which started life in the UK, in a £240m deal in December 2009.
It has reviewed its global creative and media agency relationships this year. It divided creative duties between Havas-owned Arnold and Interpublic agency Mullen in June. The next month it split its media buying and planning account between WPP's Maxus and Aegis' Carat; the former taking the US business and the latter retaining the European business and adding Canada and Mexico.
In addition to its personal care brands Alberto Culver owns a handful of food and household care brands not alluded to in Unilever's press statement this morning. They include sweetener brand SugarTwin, no-stick baking spray Baker's Joy, Mrs Dash Salt-Free Seasoning Blends, and anti-static spray Static Guard.
The acquisition is subject to the approval of regulators and Alberto Culver shareholders.