He is also socially inept, having a tendency to speak very rapidly, often babbling about tangential subjects in the middle of technical briefings (before someone impatiently brings Marshall back on to the topic at hand).

He has a fondness for unnecessary visual aids when giving a presentation, once even playing a full drum set to make a point (actor Weisman is in a rock band).

By the start of the fourth season (several months later in the timeframe of the series), he has fully recovered from his injuries and is recruited into the new Authorized Personnel Only (APO) black ops offshoot of the CIA (albeit as a 'late' addition to the organization, when they realized that they needed his computer expertise early in their first assignment).

Marshall serves as comic relief for the Alias series, but he has some serious moments when he is worried about those he cares about, including Sydney, but mostly revolving around Carrie and Mitchell.

Marshall has also discovered how hard it is to lie to those he loves, having to keep his job at APO a secret even from his wife (who appears to no longer be working for the NSA by the fourth season).

Marshall, delayed in arriving at HQ due to a problem with his baby, avoids being caught in the lockdown and becomes the only APO agent able to save Sydney.

He was later kidnapped from his home by Kelly Peyton and tortured, resisting admirably until at Sydney's urging he cooperated as part of a plan to rescue him and the also-abducted Rachel, allowing him to pass on a discreet message that would help his wife Carrie track his online activity and identify his location.

In the flash forward several years into the future presented at the end of the series finale, it is mentioned Marshall and Carrie have two more children after Mitchell, with another on the way, and all are boys.