Modigliani was born on 18 June 1918, in Rome, Italy, to the Jewish Italian family of a pediatrician father and a voluntary social worker mother.

After the passage of racial laws in Italy, in 1938, Modigliani left Italy for Paris together with his then-girlfriend, Serena Calabi, to join her parents there. After briefly returning to Rome to discuss his laurea thesis at the city’s university, he obtained his diploma on 22 July 1939, and returned to Paris.

In 1939, while they were in Paris, Modigliani married Serena Calabi. They had two children, Andre and Sergio Modigliani.

From 1942 to 1944, Modigliani taught at Columbia University and Bard College as an instructor in economics and statistics. In 1946, he became a naturalized citizen of the United States. In 1948, he joined the University of Illinois at Urbana–Champaign faculty. From 1952 to 1962, he was a member of the Carnegie Mellon University faculty.

The same year, they all emigrated to the United States and he enrolled at the Graduate Faculty of the New School for Social Research. His Ph.D. dissertation, an elaboration and extension of John Hicks’ IS–LM model, was written under the supervision of Jacob Marschak and Abba Lerner, in 1944, and is considered “ground breaking.”

The rational expectations hypothesis is considered by economists to originate in the paper written by Modigliani and Emile Grunberg in 1954.

When he was a member of the Carnegie Mellon University faculty, he formulated in 1958, along with Merton Miller, the Modigliani–Miller theorem for corporate finance. The theorem posits that, under certain assumptions, the value of a firm is not affected by whether it is financed by equity (selling shares) or by debt (borrowing money), meaning that the debt-to-equity ratio is unimportant for private firms.

In 1962, he joined the faculty of MIT, as an Institute Professor.

In 1975, Modigliani, in a paper whose co-author was his former student Lucas Papademos, introduced the concept of the “NIRU”, the non-inflationary rate of unemployment, ostensibly an improvement over the “natural rate of unemployment” concept. The terms refer to a level of unemployment below which inflation rises.

In October 1985, Modigliani was awarded the Nobel prize in Economics “for his pioneering analyses of saving and of financial markets.”

In 1985, Modigliani received MIT’s James R. Killian Faculty Achievement Award. In 1997, he received an honoris causa degree in Management Engineering from the University of Naples Federico II in 1997.

In 1997, Modigliani and his granddaughter, Leah Modigliani, developed what is now called the “Modigliani Risk-Adjusted Performance,” a measure of the risk-adjusted returns of an investment portfolio that was derived from the Sharpe ratio, adjusted for the risk of the portfolio relative to that of a benchmark, e.g. the “market.”

Modigliani died in Cambridge, Massachusetts, in 2003, while still working at MIT, and teaching until the last months of his life. Serena Modigliani-Calabi, active to the end in progressive politics, most notably with the League of Women Voters, and an outspoken believer in participatory democracy, died in 2008.