Tierney joins the agency in a newly created role and becomes its first director-level appointment since its 2006 launch.
At H&K Tierney headed up international and UK accounts as senior associate director for three years.
She will report to joint managing directors Emma Crozier and Jennie Talman, who founded the agency. The healthcare agency now employs 24 staff. It grew by six consultants during this year.
'Tamsin is joining us at an exciting time,' said Crozier. 'We have seen considerable organic growth from existing clients this year and we are optimistic about 2010.'
Tierney will be working across pan-European and UK accounts as well as strengthening Just's capabilities to implement campaigns outside of the UK.
'Despite our caution due to the uncertain economic climate going into 2009, we have had a very strong year,' said Talman. 'We have been able to focus on growing our consumer health business. Our new hires contribute to a dynamic team with an interesting mix of skills and backgrounds.'
New consumer wins for Just this year include picking up a brief with Allergan. The agency was also brought in to run a programme aimed at raising awareness of MiniCol, a cholesterol-lowering cheese from Emmi UK.
Other new appointments for the agency during 2009 include Eleanor Craven, who joined the agency from Chandler Chicco Agency. Poppy Law also came on board from Resolute, while Jessica Law joined from the Jolly Good Production Company. Antoinette Lee joined from Tonic Life, and Joanna Williams was appointed from Hill & Knowlton.
Just ranked number 13 in PRWeek's 2009 Top 25 Healthcare agencies. It also came 99th in the Top 150 PRWeek League Table.
Tierney also previously worked at Red Door Communications, Cohn & Wolfe and Ketchum.