Robinson started appearing in the web series "Campus Daze," which he also co-produced. He also guest starred in the series, "Miss Behave," in which he appeared in 3 episodes as well as "Cold Case" for one episode.
In early 2010, Brendan auditioned for the role of Mike on Pretty Little Liars, but did not get the role. He later joined the cast portraying Lucas Gottesman, the yearbook nerd who becomes involved in Hanna's life.
In 2011, his character was added for more scenes with Hanna.
In an April 2015 interview with "Fashion & Style," Robinson briefly touched on Lucas's involvement in the sixth season of Pretty Little Liars, stating that "I will hint that Lucas will be involved - but I can't say how exactly." 
|2017||Twenty five-ish||Tucker||Web Series|
|2012||How I Met Your Mother||Ned||Guest star, 1 Episode|
|2012||Review with Forrest MacNeil (Pilot)||The Intern||Guest star, 1 Episode|
|2011||Good Luck Charlie||Karl||Recurring|
|2010-2017||Pretty Little Liars||Lucas Gottesman||Recurring Season 1-present|
|2010||Miss Behave||Jordan||Multi Guest arc, 3 Episodes|
|2010||Cold Case||Evan Mazer||Guest star, 1 Episode|
|2013||Feels So Good||Allan|
|2010||The Do-Deca Pentathalon||Young Mark|
|Rid Of Me||The Young Man|
|The River Why||Kernie|