Relave replaces Patrick Widloecher, who has held the position at the State-owned group for the past two years.
La Poste said Widloecher will remain within the group and is set to take on another as-yet-unannounced role.
Vincent Relave was until now director of communications for the Paris transport system, the Regie Autonome des Transports Parisiens (RATP), which runs the French capital's rail and bus networks.
The former head of the RATP Jean-Paul Bailly was recently appointed as chairman of La Poste, where he replaces Martin Vial.
It is understood Bailly was instrumental in the hiring of Relave to La Poste's top communications role.
The French postal authority, which still maintains a monopoly over most postal services within the country, is scheduled to undergo a partial privatisation in the near future.
La Poste is struggling financially according to its recent results, posted last month. The group said it expected to see losses in the second half of the year after revealing a turnover of £5.5bn for the first half of 2002.
La Poste said it expected a loss due to a drop in turnover in the summer of 2002 and higher taxes imposed during the second half of the year.
It is widely believed the French government is planning to sell parts of La Poste in its privatisation programme.