[1] He has held editorial positions at The Washington Post and The American Prospect, and was a regular contributor to Bloomberg News and MSNBC.

[8] Klein's prolific blogging caught the attention of Steven Pearlstein, The Washington Post's veteran business columnist.

A few weeks after he heard from Pearlstein, Washington Post foreign correspondent John Pomfret asked Klein to have lunch with him and financial editor Sandy Sugawara.

[23] Klein announced he would be leaving The Washington Post in January 2014, with the intent to start a new media venture with several other veteran journalists.

[25] Klein had previously "proposed the creation of an independent, explanatory journalism website—with more than three dozen staffers" and an annual budget of more than US$10 million to remain at The Washington Post.

He frequently provides political commentary on MSNBC's The Rachel Maddow Show, Hardball with Chris Matthews, and The Last Word with Lawrence O'Donnell.

In October 2015, Klein, along with Sarah Kliff and Matt Yglesias, launched The Weeds, a Vox podcast of detailed discussions on public policy.

[12][33] According to an analysis by British digital strategist Rob Blackie, Klein was one of the most commonly followed political writers among Biden administration staff on Twitter.

"[38] Klein later said he regretted the phrasing[39] and his position is that despite universal coverage, the social determinants of health are still powerful predictors that, on average, ensure the lower socioeconomic classes die sooner than those with more income and education.

[40][41] In February 2007, Klein created a Google Groups forum called "JournoList" for discussing politics and the news media.

The forum's membership was controlled by Klein and limited to "several hundred left-leaning bloggers, political reporters, magazine writers, policy wonks and academics".

[43] Klein defended the forum saying that it "[ensures] that folks feel safe giving off-the-cuff analysis and instant reactions".

[citation needed] On June 25, 2010, Ezra Klein announced in his Washington Post blog that he would be terminating the JournoList group.

This decision was instigated by fellow blogger Dave Weigel's resignation from the Post following the public exposure of several of his JournoList emails about conservative media figures.

[46][47] Klein had justified excluding conservative Republicans from participation as "not about fostering ideology but preventing a collapse into flame war.