He previously served as a member of the Connecticut State Senate from 2003 to 2011, representing the state's 27th district in Stamford and Darien as a Democrat. McDonald resigned from the legislature on January 4, 2011 to serve as Governor Dan Malloy's chief legal counsel, a post he left to join the bench.
A Stamford native, McDonald is the son of Alex and Anne McDonald. His mother was a sixth-grade teacher who represented Stamford in the Connecticut House of Representatives from 1991 to 2003.
Andrew McDonald was educated at the Stamford Public Schools (Stark, Dolan and Stamford High School) before receiving his Bachelor's degree in Government from Cornell University, and a Juris Doctor from the University of Connecticut School of Law, where he graduated with honors. He served as Managing Editor of the Connecticut Journal of International Law and was a litigation partner with Pullman & Comley, LLC, in Stamford.
McDonald worked as Director of Legal Affairs for the City of Stamford from 1999 to 2002. He also served on the Stamford Board of Finance from 1995 to 1999, as the board's chairman from 1997 to 1999, and as Co-Chair of the Audit Committee from 1995 to 1997. He served on the Stamford Board of Representatives from the Cove from 1993 to 1995.
McDonald won narrow election to the state senate in 2002, defeating his Republican opponent, Michael Fedele (who later served as Lieutenant Governor), by 53% to 47%. He was re-elected in 2004, 2006, 2008 and 2010. He served as Deputy Majority Leader and as Senate Chair of the Judiciary Committee.
In 2006 and 2007 McDonald challenged the decision of Connecticut Chief Justice William J. Sullivan to delay publication of a court decision in an effort to promote the chief justice candidacy of his colleague, Justice Peter Zarella. Sullivan challenged the power of a legislator to subpoena him to appear at a hearing, which led to a court challenge.
In 2007 McDonald opposed a special session of the General Assembly to address parole issues following the horrific home invasion murders in Cheshire, stating "Legislating by bumper sticker motto is not the way to go." Other Democrats were more willing to respond as Congressman Chris Murphy proposal making home invasion a federal crime. McDonald relented under public pressure and a special session was held January 22, 2008 to pass laws declaring home invasion a class A felony and reforming the parole board. McDonald opposed a Three Strikes Law favored by Governor Jodi Rell to mandate life terms to career violent criminals; that measure failed to pass.
Rell reiterated her call for a Three Strikes bill on March 31, 2008 following the kidnapping and murder of an elderly New Britain woman committed by a sex offender recently released from Connecticut prison. Following the New Britain crime, McDonald lambasted the prosecutor who had handled the assailant's previous case, Waterbury State's Attorney John Connelly, who agreed to a plea bargain which sentenced the defendant to an eight-year prison term. Defense lawyer Norm Pattis called McDonald a "knucklehead" for attacking Connelly as soft on crime, noting Connelly was responsible for most of the death penalty convictions in Connecticut.
In March 2009 McDonald and Judiciary committee co-chair Mike Lawlor proposed a bill (SB 1098) to regulate the management of Roman Catholic parishes in Connecticut. The bill, by allowing parishioners to create a lay board to govern a parish, in which board all control over fiscal and administrative matters would be vested, would effectively have removed the Parish Priest and Bishop from their traditional positions of power. The bill was specific to the Catholic Church.. The public hearing on this bill was cancelled when, according to Capital Police, 1,000 supporters entered the Capital to protest. Another 4,200 were present outside the building. Opponents charged the bill would violate the separation of church and state clause in the First Amendment. It would also violate the "Supremacy clause," and the Fourteenth Amendment barring discriminatory legislation.
After two years of serving as Governor Dan Malloy's chief legal counsel, McDonald was nominated to a seat on the Connecticut Supreme Court on December 27, 2012. His nomination required the approval of the Connecticut General Assembly. The Joint Committee on Judiciary of the Connecticut General Assembly approved his nomination by a vote of 40–2 on January 14, 2013. On January 23, his nomination won the approval of the Senate by a vote of 30–3 and of the House by a vote of 125–20. He took his seat on the bench the following day.
McDonald is gay. His campaigns have won the backing of the Gay & Lesbian Victory Fund. McDonald married Charles Gray in 2009. He is one of twelve LGBT state supreme court justices currently serving in the United States.