Weddle's father fought in World War II and saw action during the Guadalcanal campaign and the Battle of Peleliu.

Weddle graduated from the USC School of Cinema, as did writing partner Bradley Thompson, whom he first met in an acting class.

A fan of Sam Peckinpah, Weddle met the director on several occasions. Weddle and his parents knew Fern Lea Peter, Peckinpah's sister, and her family. He was able to watch Peckinpah direct what would be his last film, The Osterman Weekend.

After Peckinpah's death in 1984, Weddle used Peckinpah's production files and correspondence that had been given to the Motion Picture Academy Library to write a biography of the director. This biography, The Life and Times of Sam Peckinpah was released in 1994.

It was the biography that brought Weddle to Deep Space Nine and later to Battlestar Galactica. Ira Steven Behr, a fan of Peckinpah, invited Weddle to Paramount Pictures. This enabled Weddle and Thompson to pitch stories to the show. The two joined the writing staff for DS9's final seasons. They also met and worked with producer Ronald D. Moore on the show.

Weddle and Thompson wrote twelve episodes of Deep Space Nine. Weddle can be seen in the background of the scene set at Vic Fontaine's Lounge in the final episode, "What You Leave Behind". He later wrote a DS9 novel set after the series with Jeffrey Lang. Entitled "Abyss", it focused on Section 31, the Federation's secretive intelligence service.

Weddle considers "Inquisition" to be the best Star Trek episode he and Bradley Thompson wrote, for showing "that the Federation, as perfect as it seemed, had to resort to unsavory tactics and work black bag operations to keep their world safe and pristine".

Together with Thompson, Weddle served as a story editor on the first season of Battlestar Galactica, and they became co-producers in the second season. Their responsibilities as producers increased during the third season, and they achieved supervising producer status for the fourth season.

In 2008, Thompson and Weddle joined the staff of CSI: Las Vegas mid-way through Season 9 as writers and supervising producers. As of Season 10, they are co-executive producers.

Weddle has dined and chatted at length with Jerry Lewis on his private yacht in Southern California. He appreciates Jerry Lewis as an "auteur" and wrote an article about the director and actor that appeared in the Los Angeles Times Sunday magazine section suggesting that Lewis be awarded an honorary Academy Award. Lewis won this award on February 22, 2009, though for his humanitarian achievements rather than his work in the cinema.

Deep Space Nine

• "Rules of Engagement"
• "The Assignment"
• "Business as Usual"
• "Sons and Daughters"
• "One Little Ship"
• "Inquisition"
• "The Reckoning"
• "Time's Orphan"
• "Treachery, Faith, and the Great River"
• "Prodigal Daughter"
• "'Til Death Do Us Part"
• "Extreme Measures"

Ghost Stories

• "Back Ward"
• "Beware the Muse"

The Fearing Mind

• "Upgrades"
• "Call of the Wild"
• "Maximum Security" (originally unaired)
• "On the Road" (originally unaired)

The Twilight Zone

• "Harsh Mistress"
• "Fair Warning"
• "Homecoming"

Battlestar Galactica

• "Act of Contrition"
• "The Hand of God"
• "Scattered"
• "Valley of Darkness"
• "Flight of the Phoenix"
• "Scar"
• "Downloaded"
• "Exodus"
• "Rapture"
• "Maelstrom"
• "He That Believeth in Me"
• "Revelations"
• "Sometimes a Great Notion"
• "Someone to Watch Over Me"

CSI: Crime Scene Investigation

• "The Grave Shift"
• "Kill Me If You Can"
• "A Space Oddity"
• "All In"
• "Family Affair"
• "The Lost Girls"
• "Irradiator"

Video games

• Colonial Marines

Nonfiction

• If They Move... Kill 'Em!": The Life and Times of Sam Peckinpah, a biography of noted film director Sam Peckinpah