She replaces Jenny Borgars, who is departing her role after heading the Fund since it was established in 2000. The fund's annual budget is $7.8m (£4m).
Projects currently being backed by the Development Fund include Danny Boyle's Ponte Tower, Vertigo Films' Bad Dog, spy satire Blowback with Kudos, Julian Jarrold's Brideshead Revisited with Ecosse Films, Thomas Vinterberg's How I Live Now with Passion Pictures, Sharon Maguire's Incendiary with Archer Street, and three projects with BBC Films: Coram Boy, My Week With Marilyn and Bomber.
In addition to her work on the lauded and lucrative Harry Potter franchise, Seghatchian produced Pawlikowski's My Summer Of Love and The Restraint of Beasts (the latter now in post-production), and is developing his adaptation of Vernon God Little.
She served as executive producer on Francois Ozon's Berlinale closer Angel and is developing The Curious Incident Of The Dog In The Night-Time with Heyday/Warner Bros and is working with Arnaud Desplechin's adaptation of Philip Roth's novella Deception.
UKFC CEO John Woodward said: 'Tanya has forged an exceptional reputation for finding exciting film projects and working with talent to develop scripts which work in the studio and independent film worlds and which win both audiences and awards.'