In 1977 he was sent to the Houston Astros for Cliff Johnson & Dave Bergman. In 1978 at AA Columbus he posted a 2.05 ERA with a 9-5 record for the Astros minor league team.
He began 1979 at AAA Charleston but was called up in May debuting against the San Diego Padres on May 20th. He pitched seven innings allowing just two runs, but earned no decision. In his next start he threw a complete game victory against the Cincinnati Reds allowing just one run.
Overall he appeared in 26 games, tossing three complete games, in only seven starts going 3-2 with a 3.76 ERA. He became a middle reliever, spending two seasons in Houston before going to the Pittsburgh Pirates in 1982.
After just eight games in 1983 he had a 9.22 ERA and was sent down to the minors the rest of the year to tune up. In September 1983 he was traded to the Chicago White Sox for Miguel Dilone, pitching only five games at the Sox MLB level. He was traded to the New York Mets in March of 1985 for minor leaguers Ken Reed & Gene Autrey.
At AAA Tidewater he was 11-6 with a 2.76 ERA getting a September call up to Shea Stadium. He debuted on September 17th against the Philadelphia Phillies pitching two innings of relief. He made four appearances allowing no runs in five innings of work. The next season he was forgotten through time, but was officially a member of the 1986 World Champion Mets.
He debuted in the third game of the season, as a reliever in the 12th inning of a tie game in Philadelphia. He allowed two runs in the bottom of the bottom of the 14th inning, serving up the game winning hit to Steve Jeltz.
Two days later Niemann was charged with two runs in the top of the 13th inning against the St. Louis Cardinals, taking his second loss.
On May 18th he pitched three innings of relief in Los Angeles earning the win as the Mets beat the Dodgers 8-4. As the season went on he pitched less as the talented Mets staff gave little chances & was briefly sent back down to Tidewater.
In his first game back, he pitched the first game of a double header on August 17th getting a rare start. He pitched six innings, allowing just one run against the St. Louis Cardinals earning his second win of the year in a 9-2 romp.
Overall he appeared in 31 games, getting credit for six holds, going 2-3 with a 3.76 ERA allowing 44 hits with 12 walks, while striking out 18 batters in 35 innings.
Post Season: On the field Niemann, made no post season appearances. On the rowdy flight back to New York after the Mets won the intense NLCS Game #6 against the Houston Astros
Quotes: Niemann said: "It wasn't just guys destroying a plane. It was guys destroying a plane after an emotional roller coaster. There's a difference." Niemann is credited with dousing Mets GM Frank Cashen with champagne after the victory in Houston in a famous story in the book “ The Bad Guys Won”.
He signed as a free agent with the Minnesota Twins in 1987, spending most of the year at AAA, pitching just six games with the Twins in June. He ended his playing career at age 33, Life time after eight seasons he was 7-8 with three saves, posting a 4.64 ERA with 102 strike outs in 200 innings pitched in 122 games.
Retirement: Starting in 1989 Niemann began coaching in the Mets organization. He began with Kingsport then moved on to Pittsfield in the NY/Penn. League.
In 1996 he was bullpen coach under Bobby Valentine. In June he was fired by GM Steve Phillips after an eight game losing streak. Phillips wouldn't fire the popular Valentine but decided to fire his coaching staff. He went between minor league instructor & rehab pitching coordinator.
Niemanm was the Mets AAA pitching coach for the AAA Norfolk Tides from 2005-2008.
In 2009 he replaced Guy Conti as Mets bull pen coach and remained there for 2010 under Jerry Manuel.
In May, during the subway series he got into a heated argument in view of the fans with troubled Mets closer Francisco Rodriquez in between innings while in the bullpen.
He played down the incident claiming responsibility, although K Rod seemed to have been upset at the way he was being used by Manuel. After the 2011 season he cut ties with the Mets ending a 24 year relationship with the organization
In 2012 he was the Boston Red Sox pitching coach under former Mets manager & friend; Bobby Valentine. The next year he was not retained under John Farrell's Red Sox tenure in 2013.
Niemann moved on to the St. Louis Cardinals AA Springfield team. In 2015 he won the George Kissell Award for excellence in Player development with the Palm Beach Cardinals.