Born in Utrecht, Timmer also won golf tournaments, became Dutch squash champion, played badminton and hockey.

[7] The next year he drew international attention when he was featured in the championship match for the Swiss covered courts title in St. Moritz defeating the Hungarian champion Béla von Kehrling in five sets.

[8] At the 1924 Paris Olympics he won a bronze medal in the tennis' mixed doubles event, partnering Kea Bouman.

[13] In 1926 he was the mixed doubles challenger for the international edition of the Dutch championships pairing with Irma Kallmeyer, but was overcome by the couple of Julie Stroink-Cords and De Beer.

[14] In 1929 he was a finalist of the Dutch international championships with his partner Wilbur Coen losing to the American champions Bill Tilden and Frank Hunter.

[16] A week later he met Menzel again for the singles trophy of the Grand Hotel Panhans Championships in Semmering where he was beaten in three straight sets.

[20] In mid-June he made his comeback as a runner-up for the Queen's Club Championships having it lost to Jack Crawford in four sets.

[24] Timmer found consolation in the doubles contest where he and Kehrling took revenge by defeating de Stefani and George Lyttleton-Rogers and gaining the title.

[31] Bill Tilden praised his stroke technique and described him as an all-court player, who adapted a "French" tennis style.

[33] Apart from playing tennis he also coached the Dutch royalty for free including Juliana of the Netherlands.