Ames was born in River Falls, Wisconsin, to Carleton Cecil Ames and Rachel Ames (née Aldrich). His father was a college lecturer at the Wisconsin State College-River Falls and his mother a high school English Teacher. Aldrich was the eldest of three children and the only son. In 1952, his father began working for the CIA's Directorate of Operations in Virginia, and in 1953 was posted to Southeast Asia for three years, accompanied by his family. Carleton received a "particularly negative performance appraisal" in part because of serious alcoholism and spent the remainder of his career at CIA headquarters.

Ames attended high school at McLean High School in McLean, Virginia. Beginning in 1957, following his sophomore year, he worked for the CIA for three summers as a low-ranking (GS-3) records analyst, marking Classified documents for filing. In 1959, Ames entered the University of Chicago planning to study foreign cultures and history, but his "long-time passion" for drama resulted in failing grades, and he did not finish his sophomore year. Ames worked at the CIA during the summer of 1960 as a laborer/painter. He then became an assistant technical Director at a Chicago theater until February 1962. Returning to the Washington area, Ames took full-time employment at the CIA doing the same sort of clerical jobs he had performed in high school.

Five years later, Ames completed a bachelor's degree in history at the George Washington University. Ames did not originally plan to have a career with the CIA, but after attaining the grade of GS-7 and having received good performance appraisals, he was accepted into the Career Trainee Program despite several alcohol-related brushes with the police. In 1969, Ames married fellow CIA officer Nancy Segebarth, whom he had met in the Career Trainee Program.

In 1972, Ames returned to CIA headquarters and spent the next four years in the Soviet-East European (SE) Division. His performance reviews were "generally enthusiastic", apparently because he was better at managing paperwork and planning field operations than at agent recruiting. Nevertheless, his excessive drinking was also noted, and two "eyes only" memoranda were placed in his file.

In 1976, Ames was assigned to New York City where he handled two important Soviet assets. His performance was excellent, he received several promotions and bonuses, and was ranked above most operations officers in his pay grade, although his tendency to procrastinate in submissions of financial accounting was noted. Ames' inattention to details also led him to make two important security violations, including once leaving a briefcase of Classified operational materials on the subway. Ames apparently received only a Verbal reprimand.

In 1981, Ames accepted a posting to Mexico City while his wife remained in New York. His evaluations in Mexico were mediocre at best, and he engaged in at least three extramarital affairs. In October 1982, Ames began an affair with María del Rosario Casas Dupuy, a cultural attaché in the Colombian Embassy and a CIA informant. Despite CIA regulations, Ames did not report his romance with a foreign national to his superiors, even though some of his colleagues were well aware of it. Ames' lackluster performance reviews were in part the result of heavy drinking. At a diplomatic reception in Mexico City, Ames got into a loud, drunken argument with a Cuban official that "caused alarm" among his superiors.

Nevertheless, in September 1983, the CIA assigned Ames back to the SE division in Washington. His reassignment placed him "in the most sensitive element" of the Department of Operations, which was responsible for Soviet counterintelligence. Ames had access to all CIA plans and operations against the KGB and the GRU, Soviet military intelligence. In October, Ames formally separated from Nancy, and, in November, he submitted an "outside activity" report to the CIA noting his romantic relationship with Rosario. As part of his divorce settlement, Ames agreed to pay the couple's debts plus provide Nancy monthly support for three-and-a-half years, a total of about $46,000. Ames thought the divorce might bankrupt him. Ames later said that this financial pressure was what had first led him to consider spying for the Soviet Union. Rosario also proved to be a heavy spender, phoning her family in Colombia at a cost of $400 a month and going on shopping sprees—after her arrest the FBI discovered in the Ameses' house sixty purses, more than five hundred pairs of shoes, and 165 unopened boxes of pantyhose.

Meanwhile, Ames continued to meet openly with his contact at the Soviet embassy, Sergey Dmitriyevich Chuvakhin. For a time, Ames summarized for the CIA and FBI the progress of what he portrayed as an attempt to recruit the Soviet. Ames received $20,000 to $50,000 every time the two had lunch. Ultimately, Ames received $4.6 million from the Soviets, which allowed him to enjoy a lifestyle well beyond the means of a CIA officer. When, in August 1985, Ames' divorce became final, he immediately married Rosario. Understanding that his new wealth would raise eyebrows, he developed a cover story that his prosperity was the result of money given to him by his Colombian wife's wealthy family. To help fabricate this, Ames wired considerable amounts of his espionage profits to his new in-laws in Bogota, as well as to help improve their impoverished status.

In court, Ames admitted that he had compromised "virtually all Soviet agents of the CIA and other American and foreign services known to me" and had provided the USSR and Russia with a "huge quantity of information on United States foreign, defense and security policies." It is estimated that information Ames provided to the Soviets led to the compromise of at least a hundred U.S. intelligence operations and to the execution of at least ten U.S. sources. Furthermore, Ames' betrayal of CIA methods allowed the KGB to use "controlled agents" to feed the U.S. both genuine intelligence and disinformation from 1986 to 1993. Some of this "feed material" was incorporated into CIA intelligence reports, some of which even reached three Presidents.

Prior to this, in November 1989, a fellow employee reported that Ames seemed to be enjoying a lifestyle well beyond the means of a CIA officer and that his wife's family was less wealthy than he had claimed. Nevertheless, the CIA moved slowly. When the investigator assigned to Ames' finances began a two-month training course, no one immediately replaced him. Investigators were also diverted by a false story from a CIA officer abroad who claimed that the Soviets had penetrated the CIA with an employee born in the USSR.

On February 22, 1994, Ames and his wife were formally charged by the Department of Justice with spying for the Soviet Union and Russia. Ames' betrayal resulted in the deaths of a number of CIA assets. He pleaded guilty on April 28 and received a sentence of life imprisonment. His wife received a five-year prison sentence for tax evasion and conspiracy to commit espionage as part of a plea bargain by Ames.