Ernst, who has worked for Channel 4's in-house communications agency for three-and-a-half years, will work across Amsterdam Worldwide's international clients, including Intel and Pernod Ricard.
In his new role, Ernst will report to executive creative director Richard Gorodecky, with whom he previously worked at Wieden+Kennedy.
Pernod hired Amsterdam Worldwide to handle global advertising for its Olmeca tequila brand in October last year. It has also worked on the firm's Ararat brandy product.
Gorodecky said: "Following several account wins, including Intel and Olmeca, Amsterdam Worldwide continues to seek out and attract top creative talent.
"Joseph has a proven track record delivering award-winning creative work across all platforms, and has an invaluable international perspective."
Originally qualifying as an architect, Ernst cut his creative teeth in advertising at Saatchi & Saatchi London in 2000.
Since then he has collaborated on and created campaigns for international brands such as Levis, Nike, Audi, Coca Cola, Electronic Arts, Sony, and T-Mobile at agencies including Mother London, BBH London, and Wieden+Kennedy in London, Amsterdam and Shanghai.