After a lengthy but amicable negotiation, the Nationals formally announced that Davey Johnson will return to the dugout in 2013, his final season as manager.

Both sides moved close to finalizing a deal earlier this week, ironing out the remaining details before Saturday morning’s announcement. They agreed that 2013 would be Johnson’s final season as manager and he would slide into his role as a special adviser to General Manager Mike Rizzo for the 2014 season. Since late this past season, Johnson and the Nationals had been interested in him returning next season to guide the team but the negotiations continued into early November.

“I was never really worried about it,” Johnson said in a telephone interview from his home in Winter Park, Fla., where he was taking a break from watching his beloved Texas A&M football team play Alabama after a morning of chores around the house. “It just takes longer with the process here. I think we beat last year. I’m glad it’s over.”

After a gut-wrenching loss in Game 5 of the National League Division Series, Johnson, who turns 70 in January, cited “unfinished business” and a desire to return for another season.

“We made a lot of progress from 2011 to 2012,” Johnson said. “And I was real pleased with the guys. I think we can go further. And I think a lot of inexperience caught up to us a little bit. There’s still room for this club to grow. We’ve still got some young guys that have higher ceilings. We made better steps. A lot of guys came through for being awful young. And now we have more experience and what adjustments to make to be more successful.”

Johnson said the process to finalize his deal was normal and the time was needed to change the language of his contract from a consultant to manager. Johnson took over as the Nationals’ manager in June 2011 following Jim Riggleman’s abrupt resignation. Johnson signed a three-year contract that made him a consultant for the 2013 and 2014 seasons with the agreement that the deal could be tweaked to make him the manager. The tweaks for his return next season include agreeing that this would be his final season as manager. Johnson said the decision on his retirement from managing isn’t dependent on the Nationals’ success in 2013.

“No, this is it,” he said. “We’ve still got some more growing to do. I like where we’re at. We’ve made good strides last year.”

Asked if this meant he needed to hold nothing back in order to end his managing career with a title, the ever-confident Johnson chuckled: “As usual.”

“We all kind of assumed he’d be back,” shortstop Ian Desmond said. “Anytime you have knowledge like that, and not just Davey, but our entire staff except for Bo [Porter who left for the Houston Astros], we know what we’ve got: a great clubhouse and great chemistry. Davey is definitely leading the ship.”

But Desmond held out hope that Johnson would stay at the helm longer than one season.

“I’ll believe it when I see it,” he said. “He’s a baseball man. He’s got it in his blood. … It’d be nice if he signed a five-year deal. But at the same time he’s saying he’s going to be a consultant and it’s even though he’s not going to be on the field it’s not like we’re not going to see him again.”

Johnson, who managed the Nationals to an MLB-best 98 wins and a NL East title in his first full season at the helm, is one of three finalists for the National League manager of the year award that will be announced Tuesday. He could retire with credentials that make him a Hall of Fame candidate as a manager. He has lead four different teams to the playoffs, and next year he will try to add a second World Series ring to his resume, putting it on top of the title he won managing the 1986 New York Mets.

“It’d be really great and satisfying to get him a title, now that it’ll be his final year before retirement, that he deserves for the manager he is,” catcher Wilson Ramos said.

Even though Johnson didn’t have a manager’s contract for next season until now, Johnson treated the offseason like he had before. He and Rizzo had been talking about the Nationals’ plans and strategies for next season.

One of Johnson’s foremost offseason priorities was ensuring free agent first baseman Adam LaRoche re-signs with the Nationals. Johnson has stayed in touch with LaRoche, who has made it clear he wants to return to Washington but his agents are contacting interested teams to gauge his market value. Johnson said he even bought a shipment of beef from LaRoche on Friday. LaRoche “probably made some money off me,” Johnson said, laughing.

The Nationals begin the offseason with various options on how to upgrade their roster. On Saturday, Johnson was mum about what the team needed to add over the winter, saying he would leave that to Rizzo. But he added that he liked the roster as it stood as well as the organization’s in-house options to fill the opening in the starting rotation.

“We need to do something things better and go further,” Johnson said. “There are still a lot of very important decisions to make in the spring and over the winter. I like where we’re at. Rizzo is going to be doing some things to make us stronger. I like all the guys that we have and all the insurances that we’ve got.”

The Nationals will have plenty of time to search for a manager for the 2014 season, and Rizzo has said that his preference is to promote a candidate from within the organization. Bench coach Randy Knorr is a leading in-house candidate to succeed Johnson, with first base coach Trent Jewett, Class AAA Syracuse Manager Tony Beasley and Class AA Harrisburg Manager Matt LeCroy also possibilities.

— Adam Kilgore contributed to this report.