Williams said on Tuesday that Smedley, whose radio conversations with Massa during races have made him an F1 personality, would start work before the Bahrain Grand Prix in April.
The Briton had been expected to move to Williams after Massa, with whom he had forged a close working relationship, joined the team from Ferrari at the end of 2013.
At the German Grand Prix in 2010, it was Smedley who gave Massa the message 'Fernando is faster than you' when Ferrari controversially decided to impose 'team orders' to ensure Spaniard Fernando Alonso won the race.
The order, which has gone down in Formula One lore, was devastating for Massa who had been on course for his first win since 2008 - the year before he suffered a near-fatal head injury - but finished second.
Massa's race engineer this year will be Andrew Murdoch, who worked previously with departed Venezuelan Pastor Maldonado.
Williams said Richard Lockwood had also joined the team from Marussia as head of race strategy.
Technical head Pat Symonds said the latest appointments reflected the former champions' determination to move back up the grid after a disappointing 2013 season. Williams finished ninth overall last year with a meagre five points.
"2014 gives us the biggest change to the technical regulations that I have seen in my career, and so it will be important to add further depth to the talent we already have here," Symonds said in a statement.
(Reporting by Alan Baldwin, editing by Amlan Chakraborty)
