Lezak is a specialist in the 50-meter and 100-meter freestyle races. He also owns long-course world records in the 400m freestyle and medley relays, and is a former American record holder in the 100-meter freestyle. Lezak is one of the few elite swimmers not to have a personal coach. Despite this, Lezak enjoys team sports and fellow American Gary Hall, Jr. dubbed Lezak as a "professional relay swimmer" at the 2004 Olympic Trials before their matchup in the 100-meter freestyle.
Lezak was born in Irvine, California, the son of Linda (née Mann), an elementary school science teacher, and David Lezak, a former leather goods salesman. He is Jewish. The name Lezak is pronounced Leh-Zhack (short e). Lezak attended El Camino Real Elementary School (Now Woodbury Elementary School) and Irvine High School, as well as the University of California, Santa Barbara. Lezak currently lives in Irvine with his wife, Danielle (DeAlva).
Lezak currently has competed in four Olympic Games, in 2000, 2004, 2008, and 2012 and has earned a total of Eight Olympic medals, two bronze, two silver, and four gold. He earned a spot on the U.S. team in the 2012 Games in London with a sixth-place finish in the 100-meter freestyle at the Olympic trials.
At the 2008 Summer Olympics in Beijing, Lezak was the oldest male on the U.S. swim team. He anchored the U.S. 4×100-meter freestyle relay team that won the gold medal and set a new world record. In the final 25 meters, Lezak overtook French team anchor Alain Bernard (the world record holder in the 100-meter freestyle going into the relay) to win gold despite Bernard having nearly a full body length's advantage when Lezak started his leg and half a body length with 25 meters from the end. Lezak split a 46.06, the fastest 100-meter freestyle split in history, by nearly six tenths of a second. The final time of the American team was 3:08:24, which was 3.99 seconds faster than the previous world record; the French team finished second at 3:08.32, eight one-hundredths (0.08) of a second behind—the closest finish in the event's history. This was a crucial race for Michael Phelps, because he needed it to complete the goal of winning eight gold medals in a single Olympic Games, breaking Mark Spitz's record of seven gold medals at the 1972 Olympic Games in Munich.
In short-course competitions he won five world championships, four relays plus a gold in the 100-meter freestyle in 2004. Lezak has also won seven U.S. Championships, three times in the 50-meter freestyle and four in the 100-meter freestyle.
Lezak forwent the 2009 World Aquatics Championships to compete in the 18th Maccabiah Games in Israel from July 12 to 29, 2009. Lezak was given the honor of lighting the Maccabiah torch at the Opening Ceremony. At the Maccabiah Games, Lezak won gold medals in the 50-meter freestyle, 100-meter freestyle, 4×100-meter freestyle relay, and 4×100-meter medley relay.
100 m freestyle relay split 46.06 (fastest relay split ever, although FINA does not recognize world records for relay splits, unless they were in the opening leg, because only the opening leg is done from a stationary start, whereas later swimmers can lean over in the process of diving as the preceding swimmer is coming in)