In 1976, he went to London to study photography after abandoning his studies of Economics, Law and International Affairs. It was during apprenticeships at the studios of John Vickers and Paul Nugent that he made his first attempts as a photographer. Living in an unconverted (?) floor of a hospital, without much money, he funded himself by working as a waiter. He had his hair dyed pink which helped him get noticed as a photographer and took inspiration from British celebrity fashion photographer Cecil Beaton. London was a city that allowed him to flourish expressively without the restrictions he felt were imposed on him in Peru.

Some of Testino’s most recognizable work derives from his portraits of royals, most famously, his series with Diana, Princess of Wales in 1997. Commissioned for Vanity Fair he said: “[Diana] opened a door for me because I then started photographing the royal families of Europe extensively … this brings out my love for tradition, for a way of showing family and the longevity of people”. Testino was also the official photographer for portraits of the Duke and Duchess of Cambridge on the occasion of their engagement in December 2010. In July 2015, he took the official photographs of the British Royal Family after Princess Charlotte of Cambridge’s christening at Sandringham Estate. He has photographed many other royal families in a similar fashion.

In his role as a Save the Children ambassador he helped to raise funds to build the El Salvador Clinic in the Pueblo Nuevo District, Chincha in his native Peru. The clinic was built for children with tuberculosis in the area badly affected by the devastating earthquake, which hit the coast of Peru in August 2007. The El Salvador Clinic was entirely funded from the sale of a single print from his portraits of Princess Diana, auctioned for £100,000.

Testino has been honoured for his contributions to many non-profit causes and charitable organizations through various awards and recognitions. In 2010, he was appointed one of the highest honours in his native country, The Grand Cross Order of Merit in Peru, and became President of the Board of World Monuments Fund Peru in 2014.

In 2011, he was awarded an Honorary Fellowship by The Royal Photographic Society. These are awarded to distinguished persons having, from their position or attainments, an intimate connection with the science or fine art of photography or the application thereof. In this same year GQ also awarded Testino the Man of the Year Inspiration Award.

Testino’s personal art collection has been the subject of two exhibitions. The first, Somos Libres in 2013 was at MATE – Museo Mario Testino in Lima, Peru. The second installation in 2014, Somos Libres II took place at the Pinacoteca Giovanni e Marella Agnelli in Turin, Italy. His relationship with fine art developed through frequent visits to galleries and artists studios, and he has collaborated to create works with artists such as Keith Haring, Vik Muniz, John Currin and Julian Schnabel.

In July 2013, Testino opened his first non-profit association in Barranco, Lima. Museo Mario Testino was established to act as a dynamic platform for Peruvian art through the cultivation and promotion of culture and heritage.

Testino was presented with an honorary OBE on 14 January 2014 by UK Culture Minister Ed Vaizey in recognition of his career and charity work.

In January 2018, Testino was accused by 13 male assistants and models who worked with him of sexual harassment. Models Roman Barrett, Jason Fedele and Ryan Locke complained about his behaviour during campaigns in the 1990s.

More allegations against Mario Testino came to light on 3 March 2018. Four of the five new allegations described their incidents occurring during or after 2010. Testino has denied all allegations. The total number of people publicly accusing Testino of sexual assault rose to 18.