Moore visited the Steelers earlier this week, and signing him became a priority after the Carolina Panthers lured Cotchery away with a two-year, $5 million contract.
Moore took to Twitter on Friday afternoon, saying he is "excited" to join the Steelers.
Excited to be a part of #steelernation Couldn't ask for a better organization to continue my career with!- Lance Moore (@LanceMoore16) March 21, 2014
The 5-foot-9, 190-pounder caught 37 passes for 457 yards and two touchdowns in 13 games last season. Moore's best season came in 2012, when he caught 65 passes for 1,041 yards and six touchdowns.
The addition of Moore, 30, offsets the loss of Cotchery, which had left the Steelers with little experience behind Pro Bowl wide receiver Antonio Brown.
The Saints released Moore on March 7; he had been due $3.8 million in salary and bonuses this year, including a $500,000 roster bonus due this month.
The former undrafted rookie out of Toledo ranks among the top five receivers in Saints history in receptions (346) and touchdown catches (38) to go along with 4,281 receiving yards. He was named the Saints' Man of the Year in 2012 for his work on and off the field.
Moore's role diminished last season after he missed three weeks with a hand injury. When he returned, he was used primarily as the team's No. 3 receiver, having fallen behind rookie Kenny Stills.
"While his production on paper is obvious, it only tells half the story," Saints coach Sean Payton said in a statement following the release of Moore. "Lance came to us an undrafted rookie who went to NFL Europe and spent time on our practice squad. He went on to produce outstanding results on the field for us as a result of his work ethic, reliability and commitment to get better every day. He's been one of the pillars of what we have built here as an organization."
ESPN.com Saints writer Mike Triplett contributed to this report.