Refer to "Impress the Boss" for information on how to view the contract requirements. A Championship leading team is defined as the top three in the Constructors Championship. It is possible to get this in your first season, by finishing in the top three. As long as your team doesn't expect you to finish 2nd or better in the Championship, top three will always unlock this achievement.
You can view the Constructors Championship leaderboard, by selecting "Standings" in your trailer and scrolling across to "Constructors".