Although his step-mother was a Jewish woman called Frida Cuperman, and, as a military attaché in London in the 1930s, Antonescu married a French-Jewish woman named Rasela Mendel, Antonescu was attracted to anti-Semitism early.
After his appointment in 1940 Antonescu tried to gain the friendship of Nazi Germany. In order to avoid an invasion of Soviet troops into Romania, he allowed the Wehrmacht to enter Romanian territory.
In 1941 the Iron Guard, a Romanian anti-Semitic movement that had helped Antonescu gain power, rebelled against the regime. Antonescu was able to defeat the rebellion with help from German troops. After this event he ruled as a dictator. When Germany attacked the Soviet Union, Romanian troops joined this aggression in order to regain lands that formerly had to be ceded to the USSR.
As for Antonescu's policy towards the Jews, he saved about 400,000 Jews from the fate of Hungarian Jews; 90% of all Hungarian Jews where killed.
Since he did not agree with Hitler's racist doctrines about the "master race" and his anti-semitism was largely fueled by economical nationalism, thus his policy toward them differed by region, making a distinction between the Jews in the Old Kingdom (pre-WWI Romania) and the Jews from Bessarabia. While in the Old Kingdom there were only sporadic acts of violence (the biggest being the pogrom in Iasi, where a few hundred Jews were killed by German and Romanian troups), in 1941, following the advancing Romanian Army and attacks by Jewish Resistence groups, Antonescu ordered "the deportation of all Jews" (between 80,000 and 150,000) from Bessarabia and Bukovina (who were considered "communist agents") to Transnistria, where some of them died due to the harsh conditions. In 1943 they were allowed to return to Romania.
Until 1942, he allowed and even encouraged the Zionist movement, thinking of solving the "Jewish problem" by allowing Jews to emigrate; that's how many ships sailed from Constanta towards British-controlled Palestine. This policy was canceled due to the German pressure and the British refusal to receive Jews from an enemy country in its territory.
Ion Antonescu was tried and executed by the country's subsequent communist-dominated government for alleged war crimes relating to his acceptance of German occupation (October 1940) and war against the Soviet Union.