[1] Jagielski became a communist deputy to the legislative body of Poland, the Sejm, in 1957, and he would continue to serve in that capacity for seven consecutive terms until 1985.

In 1959, he was posted to be a member of the Central Committee of the Polish United Workers' Party and appointed to be the Minister of Agriculture.

In late July 1981, Jagielski was fired from the Deputy Premiership, reportedly because he failed to produce a recovery program for the economic crisis Poland was experiencing at that time.

Jagielski was born to a peasant family[3] on 12 January 1924, in Kołomyja, Poland (Second Polish Republic) (now Kolomyia, Ukraine[4]).

[5] From 1946 to 1949, Jagielski served on the Central Board of the Związek Samopomocy Chłopskiej (Association of Peasant Self-Help), a communist organization designed to take control of the countryside.

[3] In June 1964, he became a deputy to a member of the Politburo of the Polish United Workers' Party and would hold that position until December 1971.

[6] On 21 August 1980, Mieczysław Jagielski replaced Tadeusz Pyka to lead a Polish government commission which was negotiating with strikers there.

On 26 August meeting with representatives of the strikers at the Lenin Shipyard in Gdańsk, Jagielski promised that the right to strike would be added to a new law on the official trade unions of Poland.

"[9] The agreement, as well as giving the workers of the Lenin Shipyard the right to strike, also allowed them to form their own independent trade union.

[12] In October 1980, he interacted with a delegation of Solidarity members that included Lech Wałęsa, future President of the Third Republic of Poland.

[13] Jagielski led a delegation that went to a meeting in Moscow of Comecon, the Eastern Bloc economic community, during January 1981.

[15] Unrest grew among Polish workers over the government's decision, and Jagielski negotiated with Wałęsa for six hours in the building of the Council of Ministers regarding the Saturday issue.

[15] He warned that Poland's economic troubles would increase should all Polish workers gain all Saturdays off from work, and he appealed to "the patriotism of the people".

[17] On 31 July 1981, Jagielski was fired from his position as Deputy Prime Minister, reportedly because he failed to produce a recovery program for the economic crisis Poland was experiencing at the time.