He was the youngest of Joseph and Rose Kennedy’s nine children, and the fourth son, the son of whom the least was expected. For a large part of his life, Edward M. Kennedy lived up to those low expectations. As Neal Gabler documents in his exhaustive, illuminating and sympathetic biography, “Catching the Wind: Edward Kennedy and the Liberal Hour, 1932-1975,” the first of a projected two volumes, Kennedy’s early life was a tale of missteps and woe.

But after a slow beginning and a rocky middle, during which each of the other brothers met a sudden and violent end, Edward M. Kennedy established himself as a legislative giant in the U.S. Senate, an inheritor of the idealism called forth by brothers John and Robert and a stalwart champion of New Deal liberalism. In his 47 years in the upper chamber, Kennedy sponsored 2,552 bills and saw almost 700 of them become law. By the time of his death, in 2009, he was widely recognized as the foremost lawmaker of his generation.

Particularly today, when partisan divisions in America run so deep, it’s instructive to recall Kennedy’s skill at working across party lines and gaining sufficient Republican support to secure an astonishing array of legislative achievements — in voting rights, civil rights, immigration, women’s rights, health coverage for children and access to prescription drugs. He operated by an adage his brother John had often promulgated, both in Congress and in the White House: that a sound democracy requires good-faith bargaining between the parties. Absolutists on both sides might scorn bipartisan compromise based on mutual concessions, but it’s vital to the system’s functioning. To GOP senator and presidential candidate John McCain, Ted Kennedy was “the last lion” and “the single most effective member of the Senate if you want to get results.”

Gabler’s study, when completed, will be the most detailed portrait we have of the man, and by a considerable margin. This first volume, drawing mostly on published sources and oral histories (Gabler appears to have made little use of documentary materials, including those available at the JFK Library pertaining to Ted Kennedy’s Senate years), takes the story from Kennedy’s birth, in 1932, to the gloomy autumn of 1975, a low point when many of the liberal policies he championed seemed to be under acute threat.

In the next volume, covering Kennedy’s final three decades, the senator will find greatness. But the present book, detailing his misfortunes, might have been subtitled “One Bad Thing After Another.”

A root cause of his struggles, Gabler asserts repeatedly, was the pressure of growing up in a dysfunctional home, with a domineering, often-absent father and a mother who, the author maintains, provided little love or validation. Young Teddy was chronically lonely and melancholy, we read, and then read again. Evidence for the claim is thin, and the notion fits oddly with the common perception (not entirely disavowed by Gabler, though he sees it as a “learned response”) of Teddy as a jolly and sociable youngster. Gabler’s grim depiction of the parents stands in sharp contrast with Kennedy’s own affectionate portrait of them in his poignant 2009 memoir, “True Compass.”

None of the Kennedy boys were brilliant in the classroom, but Ted struggled the most. It didn’t help that he attended 10 schools in 13 years, or that he was overweight and subject to razzing by classmates. Things improved at Milton Academy, and he did well enough there — if barely — to win admission to Harvard, where his father and his brothers had gone. Trouble soon came: In the spring of his freshman year he cheated on a Spanish exam, and the university expelled him. A stint in the Army followed, whereupon Harvard allowed him to re-enroll, but Gabler says the infraction “would hound him throughout his life and nearly eclipse his accomplishments.”

What saved him, in a way, was brother John’s successful run for the presidency in 1960. Ted oversaw the campaign in the Western states and then, in 1962, at age 30, won a special election to claim his brother’s former Senate seat in Massachusetts. The following November, JFK was assassinated, and Gabler writes movingly of the effect of the tragedy on Ted and the rest of the family. There followed Ted’s own near-death in a 1964 plane crash and, in 1968, Robert’s assassination in Los Angeles, an event that left Ted profoundly traumatized. Suddenly, he was the last brother (Joseph Jr. had been killed in World War II), burdened with the task of carrying on the Kennedy legacy, the torchbearer of a generation’s hopes and aspirations.

He was still adjusting to this role when disaster struck again. Late one summer night in 1969, in the waters off Chappaquiddick Island in Massachusetts, Kennedy left the scene of an automobile accident that killed his travel companion, Mary Jo Kopechne. Controversy swirled around the incident and Kennedy’s actions immediately afterward, and the tragedy doomed his presidential ambitions forever. Gabler goes into the episode in heavy detail, ably examining the various competing assessments of the accident and its aftermath before offering his own unambiguous summation:

“There is no credible evidence that Ted Kennedy wasn’t telling the truth. There is nothing implausible about his account, nothing in all but the most outlandish conspiracy theories to suggest that the incident was anything but a tragic accident, nothing to provide the slightest hint of a romantic liaison, nothing to suggest a cover-up. . . . And Ted himself never wavered, insisting that the skepticism about his account was ‘unwarranted and unjustified.’ ”

The years thereafter were difficult, as Kennedy and his wife, Joan, suffered growing marital strains and their son Ted Jr. was diagnosed with cancer. But gradually Kennedy began to find his place in Washington, as a thorn in the side of the Nixon administration and a shrewd legislative negotiator. Though “Catching the Wind” ends in yet another crisis moment, as Kennedy is surrounded by seething antibusing protesters in Boston, there are hints of what is to come: the maturation of a flawed but estimable public servant, wise and dedicated and determined to build a legislative legacy that would endure.

Catching the Wind

Edward Kennedy and the Liberal Hour, 1932-1975

By Neal Gabler

887 pp. $40