[2] In 7 games (4 starts) during his rookie campaign, Darnell logged an 0–2 record and 7.13 ERA with 22 strikeouts across 24 innings.

Darnell spent the entirety of the 2015 season with the Triple–A Rochester Red Wings, posting a 5–1 record and 2.78 ERA with 66 strikeouts over 35 appearances.

[5] On March 15, 2017, Darnell signed with the Somerset Patriots of the Atlantic League of Professional Baseball for the season.

Darnell started 12 games for the Double–A Montgomery Biscuits, registering a 3.98 ERA with 54 strikeouts in 74+2⁄3 innings pitched.

In 24 games (19 starts) for Harrisburg, Darnell compiled an 8–6 record and 3.91 ERA with 82 strikeouts across 112+2⁄3 innings pitched.

On April 29, 2020, Darnell signed with the Uni-President Lions of the Chinese Professional Baseball League (CPBL).