[2][3] He played in Major League Baseball (MLB) for the Cincinnati Reds, Atlanta Braves, and Baltimore Orioles.

Janish attended Cypress Creek High School where he played shortstop and pitched for the Cougars.

In 2002, he played in 61 games at shortstop, had a batting average of .299, and was named to the Western Athletic Conference All-Star team.

[5] In his first professional season, Janish batted .263 with 2 home runs and 22 RBI in 66 games for the rookie league Billings Mustangs.

Janish began the season with Louisville, hitting .293 in 35 games (4 hr, 20 rbi) before being promoted to the major league club after a string of injuries to middle infielders Alex Gonzalez, Jeff Keppinger, and Jerry Hairston Jr.

He went 3–3 with a walk as the Reds won 6–4 against the Cleveland Indians and then major league leader in ERA Cliff Lee.

[7] He delivered another clutch hit, getting a pinch-hit 2-run single to break the 7–7 tie in the 11th inning of the 18-inning game between the Reds and the San Diego Padres on May 25.

On June 26, the Reds optioned Janish to Louisville to make room for Jerry Hairston Jr., who had been activated from the disabled list.

He pitched the ninth inning of a 15–3 loss against the Milwaukee Brewers on May 6, allowing five earned runs on five hits, including a two-run homer by Prince Fielder.

[8] Janish became the starting shortstop after the August 14 trade of Alex Gonzalez to the Boston Red Sox.

He started 42 of the Reds 48 remaining games, and posted a .995 fielding percentage after the trade that led all MLB shortstops.

[8] Despite the weak bat he displayed over his first two seasons, he was slated to be the Reds starter in 2010 until they signed Orlando Cabrera during the offseason.

Janish made the Opening Day roster for the second straight year, sharing the infield backup job with Miguel Cairo.

He continued to start once or twice a week for September/October and finished the season with career highs in average (.260), home runs (5), RBI (25), on-base percentage (.338) and slugging (.385).

The Reds declined the option on Cabrera's contract and named Janish the starting shortstop for the 2011 season.

The Reds, however, made a big move by signing 2010 World Series MVP shortstop Édgar Rentería to a one-year deal.

On July 7, 2011, Janish was demoted to Triple A Louisville Bats in exchange for prospect Zack Cozart.

Manager Dusty Baker said that Janish had "put a lot of pressure on himself", "needed to get his confidence back up", and was "definitely a quality shortstop".

On July 14, he was traded to the Atlanta Braves for Todd Redmond, in order to replace the injured Andrelton Simmons.

[15] He then began his season with the Gwinnett Braves, Atlanta's AAA affiliate, before being called up on June 21 to replace the injured infielder Ramiro Peña.

[31] He had originally planned to retire when the season concluded but decided to end his playing career when he requested and received his release from the Orioles on August 21.