He was almost as powerful as Emperor Augustus.

As Augustus became older, the issue of who he wanted to succeed him as emperor became essential. Agrippa married Julia, Augustus' lone daughter, around 21 BCE. The two sons of Agrippa and Julia, Gaius and Lucius Caesar, were openly chosen by Augustus. He even adopted them as his own sons, making them both his sons and grandchildren at the same time. As a result of him displaying them across the city and assimilating them into society, the Roman public embraced them. Who Augustus had in mind as his successor was crystal clear. Agrippa was probably on Augustus' list of potential heirs before they reached adulthood, even if he wasn't the first pick.

Unquestionably, Agrippa served as Augustus' second in command. Agrippa received greater proconsular power (maius imperium proconsulare) in 18 BCE, which gave him military precedence over all other subordinate army commanders, as well as official tribunician power, which allowed him to call meetings of the Senate and People's Assembly and introduce legislation. Agrippa was referred to as Augustus' "partner in power" by the ancient historian Tacitus, who viewed tribunician authority as the "designation of supreme status" (Annals, 3.56). As a result, only Agrippa had the power to maintain the empire's stability in the event that Augustus passed away. In 23 BCE, Augustus relinquished his two consecutive terms as consul in "exchange" for these two immense powers.