The 28-year-old swapped the blue half of the San Siro to join the Rossoneri on Wednesday, with Antonio Cassano moving in the opposite direction, and he is eager to hit the ground running for Massimiliano Allegri's men.
The ex-Samp forward told the clubs website: "My first impressions were really good and the negotiations went quickly.
"I'm very happy, Milan is a top club and it would have been impossible to say no to them.
"I've got the will to win, I'm highly motivated, I want to return to being the footballer I was five months ago when I was a regular fixture in the national team.
"Sampdoria are first up and everybody knows the relationship I have with that place.
"But it's time to get off to a good start."
The recruitment of Pazzini will go some way to offsetting the loss of Cassano and the sale of Zlatan Ibrahimovic to Paris St-Germain, as last season's runners-up bid to challenge champions Juventus.
Brazilian striker Alexandre Pato will miss at least two weeks of the new campaign with a leg muscle tear.
Sampdoria were forced to return from the wilderness of Serie B through the play-offs after their shock relegation in 2011.
Ciro Ferrara has drafted in promising right-back Lorenzo De Silvestri on loan from Fiorentina with midfielder Andrea Poli making his Italy debut against England in Berne last week.
Striker Maxi Lopez may have failed to shine during a loan spell with Sunday's hosts, but Ferrara has borrowed the Argentinian from Catania regardless and should partner him with young Nicola Pozzi in attack.