His career was effectively ended after Black Panther Party leader Fred Hampton and member Mark Clark were assassinated in a raid by police coordinated by his office in 1969.

[3] Chicago mayor Richard J. Daley supported his successful bid for an appointment as United States Attorney for the Northern District of Illinois in 1964.

"[3] Running as a Democrat, he won a landslide election in 1968 for Cook County State's Attorney, winning support from White and African American voters.

[2] He ran for Mayor of Chicago in the Democratic primaries of 1975 and of 1977, losing respectively to Daley and Michael Bilandic; Hanrahan placed fourth each time.

[7] In the 1980 special election to represent the 36th ward on the Chicago City Council, Hanrahan finished third of four candidates, losing to incumbent appointee Louis Farina.