Coakley was born in Pittsfield, Massachusetts, to Edward J. and Phyllis E. Coakley. Her father was a World War II veteran, Korean War veteran, and small business owner. Her mother was a homemaker. When Coakley was one year old, she and her parents moved to North Adams. There, she attended St. Joseph’s School and Drury High School, graduating in June 1971.

Coakley graduated cum laude with a B.A. from Williams College in 1975 and a J.D. from Boston University School of Law in 1979. In the summer of 1978, while a law student, Coakley clerked for the law firm of Donovan and O’Connor of Adams, Massachusetts. After graduating from law school, Coakley began work as an associate at the law firm of Parker, Coulter, Daley & White and later practiced at Goodwin Procter—both in Boston, Massachusetts.

She joined the DA’s office in 1986 as an Assistant District Attorney in the Lowell, Massachusetts, District Court office. A year later, she was invited by the U.S. Justice Department to join its Boston Organized Crime Strike Force as a Special Attorney. Coakley returned to the District Attorney’s office in 1989 and was appointed the Chief of the Child Abuse Prosecution Unit two years later.

In 1997, while serving under Middlesex County, Massachusetts, District Attorney Tom Reilly, she and Gerry Leone led the courtroom prosecution of then 19-year-old English au pair Louise Woodward, who was later convicted in the shaking death of eight-month-old Matthew Eappen of Newton, Massachusetts.

In 1997, a special election was held for Boston’s 16th Suffolk district to replace James T. Brett, who was resigning. Five candidates, who all lived in the same Ward 16 neighborhood, including a “thoughtful, but unknown assistant DA named Martha Coakley,” entered the race. Coakley lost the race to Marty Walsh receiving 11.7% of the vote.

In December 1997, Coakley resigned her position in order to campaign for District Attorney in Middlesex County.

In 2001, Coakley successfully lobbied Acting Gov. Jane Swift to deny clemency to Gerald Amirault, a defendant in the Fells Acres Day Care Center preschool trial, whom many regarded as a victim of day care sex abuse hysteria. Clemency for Amirault had been recommended unanimously by the Massachusetts Parole Board. Amirault’s co-accused mother and sister had already been released from custody. Wall Street Journal editorial board member Dorothy Rabinowitz cites Coakley’s pursuit of the case despite lack of corroborating evidence as an example of questionable judgment on Coakley’s part.

Coakley’s actions as District Attorney in the sexual abuse case of a 23-month-old girl in 2005 have drawn sharp criticism. Coakley, who oversaw the grand jury for the case, did not immediately indict Keith Winfield, a Somerville police officer. On August 1, 2006, after a criminal complaint was threatened to be filed by Larry Frisoli, attorney for the victim’s single mother and the Republican candidate running against Coakley for Attorney General, she indicted Winfield. She requested for him to be released without cash bail. The District Attorney succeeding Coakley subsequently secured a conviction. Winfield was given two life sentences for the crime. Coakley later defended her actions by saying she acted appropriately with the evidence that was available at the time. As of 2012, film producer Steve Audette was making a documentary about Winfield’s prosecution, conviction, and continued assertion of innocence; Audette was denied access to recordings of the trial in March 2013.

Coakley was elected Massachusetts Attorney General in the 2006 general election as a Democrat, defeating Republican Larry Frisoli with 73% of the vote. She was sworn in on January 17, 2007. Coakley is the first woman to serve as Attorney General in Massachusetts.

During the Aqua Teen Hunger Force bomb scare in January 2007, Coakley was widely quoted in the press defending the reaction of Boston’s emergency services. Small electronic signs advertising a cartoon had been mistaken for bombs; Massachusetts authorities halted traffic on two bridges and closed the Charles River before realizing the signs were harmless. Coakley defended the precautions because the LED signs had looked suspicious: “It had a very sinister appearance, it had a battery behind it, and wires.”

In May 2007, Coakley testified before the Massachusetts State Legislature in support of the passage of a “buffer zone” law that created a 35-foot buffer around entrances and driveways of reproductive health care facilities that offer abortion services. The law was signed into effect by Governor Deval Patrick on November 13, 2007 and was subsequently challenged by opponents and overturned by a unanimous decision of the Supreme Court as a violation of the First Amendment.

Coakley inherited litigation of the fatal 2006 Big Dig ceiling collapse from outgoing Attorney General Tom Reilly in 2007. On March 26, 2009, she settled the final lawsuit pertaining to the incident. Through eight lawsuits attached to the incident, Coakley’s office recovered $610.625 million on behalf of the Commonwealth of Massachusetts.

In September 2008, Coakley worked with Apple Inc. and the National Federation of the Blind to have Apple redesign the popular iTunes software so it would comply with the federal Americans with Disabilities Act, as well as the Massachusetts Equal Rights Act.

In November 2008, Coakley unsuccessfully argued the case of Melendez-Diaz v. Massachusetts before the United States Supreme Court.

On February 5, 2009, she led an 18-state coalition, as well as the Corporation Counsel for the City of New York and the City Solicitor of Baltimore, urging the Environmental Protection Agency to take action in response to the 2007 U.S. Supreme Court ruling in Massachusetts v. EPA. Though the Supreme Court ruled that the EPA did have the authority to regulate greenhouse gases under the Clean Air Act, the Agency had yet to make an official decision on whether it believes that greenhouse gas emissions pose dangers to public health or welfare.

On July 8, 2009, Coakley filed a suit challenging the constitutionality of the Defense of Marriage Act. The suit claims that Congress “overstepped its authority, undermined states’ efforts to recognize marriages between same-sex couples, and codified an animus towards gay and lesbian people.” Massachusetts is the first state to challenge the legislation.

In 2009, Coakley won settlements of $60 million from Goldman Sachs and $10 million from Fremont Investment & Loan for their abuse of subprime loans and lending.

On September 1, 2009, Coakley was the first candidate to take out nomination papers to run in a special election to succeed the late Edward M. Kennedy in the United States Senate in the special election in 2010. Two days later, on September 3, Coakley officially announced her candidacy on her website. She won the Democratic primary on December 8, 2009. Her opponents were Republican Scott Brown and Libertarian Joseph L. Kennedy (no relation to the Kennedy family). Coakley was endorsed by The Boston Globe on January 14, 2010. In her last television debate January 11, 2010, at the University of Massachusetts Boston, when asked about the prospects of victory in Afghanistan, Coakley stated, “I think we have done what we are going to be able to do in Afghanistan. I think that we should plan an exit strategy. Yes. I’m not sure there is a way to succeed. If the goal was and the mission in Afghanistan was to go in because we believed that the Taliban was giving harbor to terrorists, we supported that. I supported that. They’re gone. They’re not there anymore. They’re in, apparently Yemen, they’re in Pakistan. Let’s focus our efforts on where Al Qaeda is.” This statement drew criticism from Scott Brown and his supporters, including Rudy Giuliani.

In 2010, Coakley helped draft a Massachusetts law regulating obscenity on the internet. In a decision celebrated by civil rights advocates, the law was overturned by a federal judge after a coalition of booksellers and website publishers sued, claiming the new law was unconstitutional and would hold criminally liable anyone who operates a website containing nudity or sexual material, including subjects such as art or even health information such as pregnancy or birth control. They said the law failed to distinguish between open websites and obscene material. Federal Judge Rya W. Zobel stated that the plaintiffs demonstrated “without question that the law violated the First Amendment by infringing on and inhibiting free speech.

On January 19, 2010, Coakley was defeated by Brown 52% to 47% in the special election. Brown received 1,168,107 votes, Coakley received 1,058,682 votes, and Joseph L. Kennedy received 22,237 votes.

On September 15, 2013, WCVB-TV learned of Coakley’s intention to run for the Massachusetts governorship when incumbent Democrat Deval Patrick retired in 2014. Coakley was set to formally announce her entry into the race the following Monday. She won the Democratic nomination on September 9, 2014. On November 4, 2014, she was narrowly defeated in the general election for governor by Republican Charlie Baker, who was endorsed by the Boston Globe despite the Globe’s having endorsed Coakley four years prior in her Senate campaign.

From 2015 through early 2019, Coakley worked for Foley Hoag, a Boston-based law firm, as a lawyer and lobbyist. While at the firm, Coakley represented the fantasy sports website DraftKings and student-loan firm Navient when state governments were examining the practices of these industries.

In April 2019, it was announced that Coakley had taken a full-time role with electronic cigarette maker Juul on their government affairs team. As a former attorney general, lobbying attorneys general for the vaping industry has called into question the ethics of Coakley’s work for Juul, a leader in the electronic cigarette industry accused of marketing addictive nicotine products to youths.

During Coakley’s tenure as Attorney General, misconduct at Massachusetts’ crime laboratories led to the reexamination of tens of thousands of drug convictions. Chemist Annie Dookhan was accused of forging reports and tampering with samples to produce desired results. Similarly, Sonja Farak was accused of tampering with the evidence she was tasked with analyzing by using it to get high herself. The actions of both women, who acted independently, resulted in tens of thousands of drug counts being dismissed, the largest single mass dismissal of criminal cases in U.S. history. How to Fix a Drug Scandal is an American true crime documentary miniseries that was released on Netflix on April 1, 2020 that tells the story of Erin Lee Carr, who followed the aftereffects of this notorious case. How to Fix a Drug Scandal depicts the role of Martha Coakley, who was accused of political cover up.