His time there was interrupted by a two-year enlistment in the Army where he pitched for the military baseball team on Fort Meade, Maryland.

Relying on a good fastball and slider, Brosnan enjoyed a career best season with the Reds in 1960, when he compiled an 8–3 record and a 2.36 ERA.

[2] In 1961, the Reds won the National League pennant and played the New York Yankees in the World Series, Brosnan's only post-season appearance.

The Reds, facing a formidable Yankees team led by Mickey Mantle and Roger Maris, lost in five games.

[4] While known as a moderately effective pitcher, both as a starter and a reliever, Brosnan gained greater fame by becoming one of the first athletes to publish a candid personal diary.

[2] Two years later, Brosnan again kept a diary, a fortuitous circumstance as the Reds would win the National League championship in 1961, before falling to the New York Yankees in the World Series.

"[4] Writing in the Chicago Tribune in July 1960, then-White Sox president Bill Veeck acknowledged that The Long Season was "delightful", but that "Brosnan has his say about many who may have, in times past, had their say about him.

He worked for several years as a sports anchor in the Chicago area and delivered sportscasts for the Chicago-area radio station WFYR.

-- Washington Post book critic Jonathan Yardley[2]Brosnan was inducted into the Baseball Reliquary's Shrine of the Eternals in 2007.