Ross' rendering style, his attention to detail, and the perceived tendency of his characters to be depicted staring off into the distance has been satirized in Mad magazine.

Alex Ross first became enamored of superheroes as a child, when he saw Spider-Man on the children's TV series The Electric Company.

He was an illustration student at Chicago's American Academy of Art.

Before breaking into comics, Ross worked as a storyboard artist. His first published work was the 1990 five-issue miniseries, Terminator: The Burning Earth, written by Ron Fortier and published by NOW Comics. Ross created all of the art, from pencils through coloring for the series. He performed similar work on a variety of titles over the next few years. In 1993, he completed his first painted superhero assignment, the cover of a Superman novel, Superman: Doomsday & Beyond.

During this time, Ross met writer Kurt Busiek, and the two began submitting proposals for series that would feature paintings as their internal art. Marvel agreed to a project that would tell much of the history of the Marvel Universe from the perspective of an ordinary person. That limited series, Marvels, was released in 1994, and chronicled the life of a photojournalist, as he reacted to living in a world of superheroes and villains.

Busiek, Ross, and penciller Brent Anderson went on to create Astro City, first published by Image Comics in 1995 and later by Wildstorm Comics. The series features an original superhero world and continues the theme of Marvels, exploring how ordinary people, superheroes and villains react to a world where the fantastic is commonplace. Ross paints the covers and helps set the costumes and the general look and feel for the series, which has been published sporadically in recent years.

In 1996, Ross worked with writer Mark Waid on the DC Comics limited series Kingdom Come, which presents a possible future for the DC universe, in which Superman and several other classic superheroes return from retirement to tame a generation of brutal anti-heroes. The work featured Ross' redesigned versions of many DC characters, as well as a new generation of characters.

Ross followed Kingdom Come with Uncle Sam, a non-superhero work for DC's Vertigo line, an experimental work that examined the dark side of American history.

In the early 2000s, with writer Jim Krueger, Ross plotted and designed characters for a trilogy of Marvel limited series, Earth X, Universe X, and Paradise X, which combined dozens of Marvel characters from various time periods.

Between 1998 and 2003, writer Paul Dini and Ross produced annual tabloid-sized editions celebrating the 60th anniversaries of DC Comics' Superman (Peace on Earth), Batman (War on Crime), Shazam (Power of Hope), and Wonder Woman (Spirit of Truth), as well as two specials featuring the Justice League, Secret Origins and Liberty and Justice.