The agency picked up the business following a five-way pitch against undisclosed agencies. The Gate was the previous incumbent on the account.
The Leith Agency will work closely with sister consultancies Stripe Communications and Blonde Digital, as well as the "See me" in-house marketing team, to produce an integrated campaign that will look to challenge the stigma associated with mental ill-health.
Launched in 2002, "See me" is run by an alliance of five Scottish mental health organisations.
The body is fully funded by the Scottish Government, as part of its commitment to improving mental health and well-being.
Suzie Vestri, the campaign director at "See me", said: The next two years is a very exciting phase for "See me" so it was vital that we work with an agency that not only recognises the importance of the next chapter, but can also take the campaign in a fresh, new direction."