He was ordained back in 1984. His first assignment was as an assistant parish priest in Germany.
MSGR. GEORG GAENSWEIN
Benedict XVI's Personal Secretary
"I've been a priest for 28 years now. After my ordination, I was sent to a parish in a German town in the Black Forest. That's actually where I'm from and it's located on the border with France.”
In 1993, after completing his doctorate in Canon Law in the city of Munich, he moved to Rome. Two years later, in 1995 he started working at the Vatican, at the Congregation for Divine Worship and the Discipline of the Sacraments. A year later, he started working at the Congregation for the Doctrine of the Faith, where Cardinal Joseph Ratzinger was Prefect.
In 2003, the Cardinal and future Pope made Gaenswein his personal secretary, which continued when Ratzinger was elected Pope in 2005.
Aside from always accompanying the Pope, he was recently named the Prefect of the Papal Household, which means he helps organize the Popes daily schedule.
Since that job is part of the Holy See's hierarchy, the Prefect of the Papal Household, should be a bishop. So to fulfill that requirement, he will be ordained a bishop by Benedict XVI on January 6th.
Under that title, he will hold the titular see of the small Italian town of Urbisaglia, whose patron saint is actually St. George. That diocese did exist at one point, but now only its title remains. Usually it's granted to bishops within the Roman Curia.
After 18 years at the Vatican, Gaenswein's appointment is yet another sign of the confidence, Benedict XVI has in him.