Yuli Markovich Daniel (Russian: Ю́лий Ма́ркович Даниэ́ль, IPA: [ˈjʉlʲɪj ˈmarkəvʲɪtɕ dənʲɪˈelʲ] ^ⓘ; 15 November 1925 – 30 December 1988) was a Russian writer and Soviet dissident known as a defendant in the Sinyavsky–Daniel trial in 1966.

Daniel wrote and translated works of stories and poetry critical of Soviet society under the pseudonyms Nikolay Arzhak (Russian: Никола́й Аржа́к, IPA: [nʲɪkɐˈlaj ɐrˈʐak] ^ⓘ) and Yu. Petrov (Russian: Ю. Петро́в, IPA: [ˈju pʲɪˈtrof] ^ⓘ) published in the West to avoid censorship in the Soviet Union. Daniel and Andrei Sinyavsky were convicted of anti-Soviet agitation in a show trial, becoming the first Soviet writers convicted solely for their works and for fiction, serving five years at a labour camp.

Yuli Daniel was born on 15 November 1925 in Moscow, Soviet Union, the son of the Russian Jewish playwright Mark Daniel and Minna Pavlovna Daniel. In 1942, the 17-year-old Daniel lied about his age and volunteered to serve on the 2nd Ukrainian Front and the 3rd Belorussian Front during Eastern Front of World War II. In 1944, Daniel was critically wounded in his legs and was demobilized from the Red Army. In 1950, Daniel graduated from the Moscow Pedagogical Institute (now Moscow State Regional University), and went to work as a schoolteacher in Kaluga and Moscow.

Daniel also published translations of verse from a variety of languages, and like his friend Andrei Sinyavsky, wrote topical stories and novellas which sometimes satirised or were critical of Soviet society but were, naturally, rejected for publication by the Communist Party of the Soviet Union (CPSU) during a time of extreme censorship in the Soviet Union. Daniel and Sinyavsky smuggled their works out of the Soviet Union as samizdat to France to be published under pseudonyms. Daniel married Larisa Bogoraz, who later also became a celebrated Soviet dissident.

Daniel's work Moscow Speaking, published in 1959 under the pseudonym Nikolai Arzhak, caught the attention of the KGB, the main security agency and secret police of the Soviet Union. The KGB began investigating Daniel and Sinyavsky's dissident works being published in the West, and soon linked their pseudonyms to their real identities. Daniel and Sinyavsky were placed under constant surveillance and investigation by the KGB for several years.

In September 1965, Daniel and Sinyavsky were arrested and tried in the infamous Sinyavsky-Daniel trial for their literary works published abroad. The Soviet prosecution could not charge Daniel and Sinyavsky for publishing material abroad or using pseudonyms as both were legal under Soviet Law. Instead they were charged with the offense of anti-Soviet agitation and propaganda under Article 70 of the RSFSR Criminal Code. Both writers entered a plea of not guilty, which was unusual for defendants in Soviet show trials. On February 14, 1966, Daniel was sentenced to five years of hard labor for "anti-Soviet activity" while Sinyavsky was sentenced to seven years.

In 1967, Andrei Sakharov appealed on behalf of Daniel directly to Yuri Andropov, at the time Chairman of the KGB. Sakharov was told that both Daniel and Sinyavsky would be released under a general amnesty on the fiftieth anniversary of the October Revolution, but this turned out to be false as the amnesty did not apply to political prisoners. Daniel spent four years of captivity at the Dubravlag, a Gulag camp in Mordovia, and one year in Vladimir Prison.

Daniel was released and refused to emigrate, as was customary among Soviet dissidents, and lived in Kaluga before moving to Moscow.