The two sides were expected to sign the deal by Thursday morning, a league source told ESPN.
"Our officials will be back on the field starting tomorrow night" for the Cleveland-Baltimore game, Commissioner Roger Goodell said. "We appreciate the commitment of the NFLRA in working through the issues to reach this important agreement."
The two sides concluded two days of talks with the announcement of a tentative eight-year deal, which must be ratified by 51 percent of the union's 121 members. They plan to vote Friday.
The agreement brings to an end three weeks of play with the replacement refs, who triggering a wave of frustration that threatened to disrupt the rest of the season. In particular was a missed call that cost the Green Bay Packers a win on a chaotic final play at Seattle on Monday night. The closest official to the play, at the back of the end zone, signaled for the clock to stop, while another official at the sideline ran in and then signaled touchdown.
The union was seeking improved salaries, retirement benefits and other logistical issues for the part-time officials. The NFL has proposed a pension freeze and a higher 401(k) match, and it wants to hire 21 more officials to improve the quality of officiating.
The union has fought that, fearing it could lead to a loss of jobs for some of the current officials, as well as a reduction in overall compensation.
"The long-term future of our game requires that we seek improvement in every area, including officiating," Goodell said in a statement. "This agreement supports long-term reforms that will make officiating better. The teams, players and fans want and deserve both consistency and quality in officiating."
ESPN and the Associated Press contributed to this report.