Lee, who was at an event on Monday and appeared in good health, had served as mayor since 2011.
Here's a look back at Lee's career in photos.
President Barack Obama walks with San Francisco Mayor Ed Lee after arriving at San Francisco International airport in San Francisco, Tuesday, Oct. 25, 2011. (Eric Risberg/AP Photo)
Mayor Ed Lee, center, speaks at a news conference next to his wife Anita, right, and his daughter Brianna outside of his office at City Hall, Wednesday, Nov. 9, 2011. (Jeff Chiu/AP Photo)
This undated image shows San Francisco Mayor Ed Lee during his time with the Asian Law Caucus. (Asian Law Caucus)
This image from the early 1980s shows San Francisco Mayor Ed Lee during his time with the Asian Law Caucus. (Asian Law Caucus)
This undated image shows San Francisco Mayor Ed Lee during his time with the Asian Law Caucus. (Asian Law Caucus)
This image shows San Francisco Mayor Ed Lee during his time with the Asian Law Caucus in 1988. (Asian Law Caucus)
This undated image shows San Francisco Mayor Ed Lee during his time with the Asian Law Caucus. (Asian Law Caucus)
This undated image shows San Francisco Mayor Ed Lee during his time with the Asian Law Caucus. (Asian Law Caucus)
This undated image shows San Francisco Mayor Ed Lee during his time with the Asian Law Caucus. (Asian Law Caucus)
Mayor Ed Lee applauds after presenting a key to the city to Giants pitcher Matt Cain in honor of Cain's perfect game against the Houston Astros, during a ceremony, June 26, 2012. (Jeff Chiu/AP Photo)
''Batkid',' 5-year-old leukemia patient Miles Scott, stands next to Batman as he receives the key to the city from Mayor Ed Lee, at a rally outside of City Hall Nov. 15, 2013. (Jeff Chiu/AP Photo)
Hillary Rodham Clinton, right, waves next to San Francisco Mayor Ed Lee after visiting Red Blossom Tea Company in Chinatown in San Francisco, Wednesday, May 6, 2015. (Jeff Chiu/AP Photo)
Torch runners Andrea Vincent, left, and Ed Lee hold the torch Wednesday, April 9, 2008 during the Torch Relay in San Francisco. (Carlos Avila Gonzalez, Pool/AP Photo)
Oakland Mayor Jean Quan, left, San Jose Mayor Chuck Reed and SF Mayor Ed Lee, right, laugh at the 8th Annual CEO Summit at IBM offices in San Jose, Calif., Friday, April 22, 2011. (Paul Sakuma/AP Photo)
San Francisco interim mayor Ed Lee smiles as his daughter, Brianna, right, looks on at his campaign headquarters for mayor in San Francisco, Tuesday, Nov. 8, 2011. (Paul Sakuma/AP Photo)
Mayor Ed Lee speaks at a panel at the Silicon Valley Leadership Group's 9th Annual CEO Business Climate Summit in San Jose, Calif., Tuesday, April 24, 2012. (Jeff Chiu/AP Photo)
San Francisco Mayor Ed Lee waves during the 44th annual Gay Pride parade Sunday, June 29, 2014, in San Francisco. (Eric Risberg/AP Photo)
San Francisco Mayor Ed Lee waves during a parade for the Golden State Warriors winning the NBA championship in Oakland, Calif., Friday, June 19, 2015. (Jeff Chiu/AP Photo)
Mayor Ed Lee speaks during a meeting at City Hall by city leaders and community activists to reaffirm the city's commitment to being a sanctuary city, Nov. 14, 2016. (Jeff Chiu/AP Photo)
Mayor Ed Lee laughs as he talks with Golden State Warriors general manager Bob Myers during an NCAA college basketball game between San Francisco and Gonzaga, Jan. 5, 2017. (Jeff Chiu/AP Photo)
Warriors president & COO Rick Welts, listens to speakers next to San Francisco Mayor Ed Lee and owner & CEO Joe Lacob during a ceremony for the Chase Center, Jan. 17, 2017. (Jeff Chiu/AP Photo)
Mayor Ed Lee listens to questions during a news conference at City Hall Tuesday, Aug. 15, 2017, in San Francisco. (Eric Risberg/AP Photo)
San Francisco Mayor Ed Lee passed away suddenly Tuesday morning after going into cardiac arrest on Monday night. He was 65 years old.
Lee, who was at an event on Monday and appeared in good health, had served as mayor since 2011.
Here's a look back at Lee's career in photos.
Lee, who was at an event on Monday and appeared in good health, had served as mayor since 2011.
Here's a look back at Lee's career in photos.